Game: Grab yourself a seat, friend.

Looking over the altar, you find a small hidden compartment blended into the front of it. Looking over to Silene to ask your question, you notice something off about the wall a couple feet away as well.

Going to the oddity in the wall, you hear a slight echo of the waterfall. You find the jagged looking wall is actually collapsed rubble, that has sat here undisturbed for ages.

The rubble seems to have congealed together over time, making sort of a makeshift "door", that with enough people pushing it will easily move with no other trouble.

The false wall slightly budges, you gather it would only take one or two other to push it.

Nothing happens, it doesn't even feel as if you're poking a hidden compartment but part of a solid altar.

Between Elnorath and Ramiel, the false wall just needs a little extra push, Izen's stout muscular body is more than enough to move it out of the way and then some. With the false wall removed, it reveals a tunnel.