When I was thirteen and my little sister was ten, the two of us travelled by ourselves to Yamanashi Prefecture during summer vacation. Our mother’s brother worked in a research lab at a university in Yamanashi and we went to stay with him. This was the first trip we kids had taken by ourselves. My sister was feeling relatively good then, so our parents gave us permission to travel alone.

Our uncle was single (and still is single, even now), and had just turned thirty, I think. He was doing gene research (and still is), was very quiet and kind of unworldly, though an open, straightforward person. He loved reading and knew everything about nature. He enjoyed taking walks in the mountains more than anything, which, he said, was why he had taken a university job in rural, mountainous Yamanashi. My sister and I liked our uncle a lot.

Backpacks on our backs, we boarded an express train at Shinjuku Station bound for Matsumoto, and got off at Kofu. Our uncle came to pick us up at Kofu Station. He was spectacularly tall, and even in the crowded station we spotted him right away. He was renting a small house in Kofu along with a friend of his, but his roommate was abroad so we were given our own room to sleep in. We stayed in that house for a week. And almost every day we took walks with our uncle in the nearby mountains. He taught us the names of all kinds of flowers and insects. We cherished our memories of that summer.

One day we hiked a bit farther than usual and visited a wind cave near Mt. Fuji. Among the numerous wind caves around Mt. Fuji this one was the largest. Our uncle told us about how these caves were formed. They were made of basalt, so inside them you heard hardly any echoes at all, he said. Even in the summer the temperature remained low; in the past people stored ice they’d cut in the winter inside the caves. He explained the distinction between the two types of caves: fuketsu, the larger ones that were big enough for people to go into, and kaza-ana, the smaller ones that people couldn’t enter. Both terms were alternate readings of the same Chinese characters meaning “wind” and “hole.” Our uncle seemed to know everything.

At the large wind cave, you paid an entrance fee and went inside. Our uncle didn’t go with us. He’d been there numerous times, plus he was so tall and the ceiling of the cave so low he’d end up with a backache. “It’s not dangerous,” he said, “so you two go on ahead. I’ll stay by the entrance and read a book.” At the entrance the person in charge handed us each a flashlight and put yellow plastic helmets on us. There were lights on the ceiling of the cave, but it was still pretty dark inside. The deeper into the cave we went, the lower the ceiling got. No wonder our lanky uncle had stayed behind.

My kid sister and I shone the flashlights at our feet as we went. It was midsummer outside—ninety degrees Fahrenheit—but inside the cave it was chilly, below fifty. Following our uncle’s advice, we were both wearing thick windbreakers we’d brought along. My sister held my hand tightly, either wanting me to protect her or else hoping to protect me (or maybe she just didn’t want to get separated). The whole time we were inside the cave that small, warm hand was in mine. The only other visitors were a middle-aged couple. But they soon left, and it was just the two of us.

My little sister’s name was Komichi, but everyone in the family called her Komi. Her friends called her Micchi or Micchan. As far as I know, no one called her by her full name, Komichi. She was a small, slim girl. She had straight black hair, neatly cut just above her shoulders. Her eyes were big for the size of her face (with large pupils), which made her resemble a fairy. That day she was wearing a white T-shirt, faded jeans, and pink sneakers.

After we’d made our way deeper into the cave, my sister discovered a small side cave a little way off the prescribed path. Its mouth was hidden in the shadows of the rocks. She was very interested in that little cave. “Don’t you think it looks like Alice’s rabbit hole?” she asked me.

My sister was a big fan of Lewis Carroll’s “Alice’s Adventures in Wonderland.” I don’t know how many times she had me read the book to her. Must have been at least a hundred. She had been able to read since she was little, but she liked me to read that book aloud to her. She’d memorized the story, yet, still, each time I read it she got excited. Her favorite part was the Lobster Quadrille. Even now I remember that part, word for word.

“No rabbit, though,” I said.

“I’m going to peek inside,” she said.

“Be careful,” I said.

It really was a narrow hole (close to a kaza-ana, in my uncle’s definition), but my little sister was able to slip through it with no trouble. Most of her was inside, just the bottom half of her legs sticking out. She seemed to be shining her flashlight inside the hole. Then she slowly edged out backward.

“It gets really deep in back,” she reported. “The floor drops off sharply. Just like Alice’s rabbit hole. I’m going to check out the far end.”

“No, don’t do it. It’s too dangerous,” I said.

“It’s O.K. I’m small and I can get out O.K.”

She took off her windbreaker, so that she was wearing just her T-shirt, and handed the jacket to me along with her helmet. Before I could get in a word of protest, she’d wriggled into the cave, flashlight in hand. In an instant she’d vanished.

A long time passed, but she didn’t come out. I couldn’t hear a sound.

“Komi,” I called into the hole. “Komi! Are you O.K.?”

There was no answer. With no echo, my voice was sucked right up into the darkness. I was starting to get concerned. She might be stuck inside the hole, unable to move forward or back. Or maybe she had had a convulsion in there and lost consciousness. If that had happened I wouldn’t be able to help her. All kinds of terrible scenarios ran through my head, and I felt choked by the darkness surrounding me.

If my little sister really did disappear in the hole, never to return to this world, how would I ever explain that to my parents? Should I run and tell my uncle, waiting outside the entrance? Or should I sit tight and wait for her to emerge? I crouched down and peered into the hole. But the beam from my flashlight didn’t reach far. It was a tiny hole, and the darkness was overwhelming.

“Komi,” I called out again. No response. “Komi,” I called more loudly. Still no answer. A wave of cold air chilled me to the core. I might lose my sister forever. Perhaps she had been sucked into Alice’s hole, into the world of the Mock Turtle, the Cheshire Cat, and the Queen of Hearts. A place where logic did not apply. We never should have come here, I thought.

But finally my sister did return. She didn’t back out like before but crawled out head first. Her black hair emerged from the hole first, then her shoulders and arms, and finally her pink sneakers. She stood in front of me, without a word, stretched, took a slow, deep breath, and brushed the dirt off her jeans.

My heart was still pounding. I reached out and tidied her dishevelled hair. I couldn’t quite make it out in the weak light inside the cave, but there seemed to be dirt and dust and other debris clinging to her white T-shirt. I put the windbreaker on her and handed her the yellow helmet.

“I didn’t think you were coming back,” I said, hugging her to me.

“Were you worried?”

“A lot.”

She grabbed my hand tightly. And, in an excited voice, she said, “I managed to squeeze through the narrow part, and then, deeper in, it suddenly got lower, and down from there it was like a small room. A round room, like a ball. The ceiling was round, the walls were round, and the floor, too. And it was so, so silent there, like you could search the whole world and never find any place that silent. Like I was at the bottom of an ocean, in a crater that went even deeper. I turned off the flashlight and it was pitch dark, but I didn’t feel scared or lonely. That room was a special place that only I’m allowed into. A room just for me. No one else can get there. You can’t go in, either.”

“ ’Cause I’m too big.”

My little sister bobbed her head. “Right. You’ve gotten too big to get in. And what’s really amazing about that place is that it’s darker than anything could ever be. So dark that when you turn off the flashlight it feels like you can grab the darkness with your hands. Like your body is gradually coming apart and disappearing. But since it’s dark you can’t see it happen. You don’t know if you still have a body or not. But even if, say, my body completely disappeared, I’d still be there. Like the Cheshire Cat’s grin staying on after he vanished. Pretty weird, huh? But when I was there I didn’t think it was weird at all. I wanted to stay there forever, but I thought you’d be worried, so I came out.”

“Let’s get out of here,” I said. She was so worked up it seemed as if she were going to go on talking forever, and I had to put a stop to that. “I can’t breathe well in here.”

“Are you O.K.?” my sister asked, concerned.

“I’m O.K. I just want to go outside.”

Holding hands, we headed for the exit.

“Do you know?” my sister said in a small voice as we walked, so no one else would hear (though there wasn’t anyone else around). “Alice really existed. It wasn’t made up. It was real. The March Hare, the Mad Hatter, the Cheshire Cat, the Playing Card soldiers—they all really exist.”

“Maybe so,” I said.

We emerged from the wind cave, back into the bright real world. There was a thin layer of clouds in the sky that afternoon, but I remember how terribly glaring the sunlight seemed. The screech of the cicadas was overpowering, like a violent squall drowning everything out. My uncle was seated on a bench near the entrance, absorbed in his book. When he saw us, he grinned and stood up.