TLDR: it was fantastic and worth the trip. Wear a fleece because you will get dripped on and it’s very chilly in the cave. If you can usually fit into tight spaces, take the extra ¥200 route. Take the time to visit the nearby observatory.

Pro tips: Suica cards don’t work on this stop of the JR train line, and Kammata’s train ticket booth is only open a few hours per day, so purchase a paper ticket to get there and expect to stop by a ticket window somewhere else down the line on your way back.

There are coin lockers outside the cave’s ticket booth. You’ll get your ¥100 back if you use the small locker.

The observatory gift shop has some items that are identical to the cave gift shop, but a few hundred yen cheaper.

Full version: Absolutely would go again. We live in Japan and took a day-trip to visit the cave. Had no idea it was such a picturesque location. We took trains to Kammata station and then took the 5 minute taxi drive to the cave. For us the trip was easy. 2 adults, plus an 8 year old and an 11 year old.

We paid for the extra ¥200 cave excursion. We had to squat low and shuffle a few times to get past one or two very low-hanging cave features, but it really added to the adventure. For the non-shape-shifters, stick to the regular route. Expect stairs, some narrow passages, and damp floors. You will have to touch the cave walls in places in order to get through safely.

The cave routes have an amazing variety of formations, and plenty of them. It didn’t matter where we looked, there was something to see. There are a few places in the cave where you can push a button to add lighting, and there is a special area where the lighting cycles through phases. It’s all done in excellent taste, and the cave and surrounding area is extremely well maintained.

You can go at your own pace. We spent about 1.5 hours in the cave.

The cave exit is separate from the entrance, and guides you out to a Japanese garden with a fountain and koi pond. If you go early you can pay ¥100 to feed the fish.

Not far from the garden is the gift shop, with a restaurant above it. The food was excellent and quickly served, and the view was incredible, with giant picture windows that let us watch the weather roll over the mountains, the small playground, and the lavender garden growing on the slope. Lots of fun things in the gift shop, but do check out the observatory shop first for the best deals.