As Medulas is a small town outside Ponferrada located right at the site where the Romans let loose with a ton of water and blew the insides out of mountains as they searched for gold. The town is dedicated exclusively to tourism surrounding the site. There is one ugly modern box hotel and one "rural hotel" Agoga which is pleasant, quiet, surrounded by green yards and flowers. (single room with breakfast about 45 E).
There is a nice, but small visitors center, which is very informative. Without it, I would have had no idea where all these strange formations came from. Some artifacts, some models, some short movies.
The prime attraction is walking around the area. There are well marked, car-free paths that lead up and down, both through the maze of "leftover mountain innards" and up to some incredible, spectacular even, viewpoints over the entire site. I have never seen anything like this and I understand how it made its way onto the UNESCO world heritage list.
Though it's well off the beaten path, it is worth a trip for anyone who is visiting the Bierzo or lower Galicia.