Reading the following claims, I'm not totally convinced that the entrance is underwater...Posted by Bill Ryan (here)
[...] it's claimed the library can be reached -- via an underwater entrance to the cave system.
Posted by Stan Grist
The secret entrance is only accessed from underwater!Posted by Gaston Fernández Borrero
According to the story, they had to dive down a few meters, swim a short distance under the water and come up into a small cavePosted by Stanley Hall
Jaramillo always said that the entrance was under the river [...] Entrance is gained through an underwater opening in a river [...] whenever diving equipment was discussed as a necessity Petronio would say that even though it [the entrance to the cave] was under the river, it did not mean we would get wet.Posted by Petronio Jaramillo (according to Pino Turolla)
Finally we climbed over the top of another small plateau and looked down and saw at our feet a good-sized stream. We jumped into it from a considerable height—something I had never done before in my life—and crossed it. Then we came to what looked like the entrance to a small cave. But as we entered it, leaving the water behind us, I realized I was treading on steps made in perfect symmetry.