We spent a very enjoyable afternoon at the Las Hornillas Volcano Activity Center. After a delicious lunch (cosada con pescado) we took the tractor ride into the rainforest, which was lots of fun. The hike to the waterfalls was beautiful. The suspension bridges provide unique access and great views of the river and the falls, and the rainforest is breathtaking. The waterfalls are very dramatic (it's the rainy season, so there was plenty of water), and the vegetation was spectacular.
The area of volcanic activity, while small, was still very dramatic. The sauna, baths, hot springs and mud baths were very relaxing and everyone who worked there was extremely friendly and helpful. Our van had a mechanical problem, and one of the young men spent quite a bit of time helping us to get it running again.
This was a great afternoon in a place that felt decidedly non-touristy. I highly recommend it.