How do I get down from the floating ledge in the arch room in Fez?

Question

In the early, blue-sky area of the game, there's a room with a stone arch and two treasure chests. One of the chests is on top of the arch, but the other is on a floating ledge far to the side. This is the room Gomez enters at 3:35 in Polytron's trial gameplay video, though the ledge doesn't appear in the video (I guess it's only in the full game?).

Once you get over to the floating ledge, how do you get back down? It looks like all the ledges you can jump to are too far down to survive, and this room doesn't have water.

Answer 1

In the full game, there is a treasure map (you can look at both side of the map by rotating it the same way you change perspective during the game) explaining how to get there.

There is no ledge, even in the full game, only invisible platforms.

Not sure if the trial version has treasure maps though.

Answer 2

A treasure map shows the hidden platforms on the "broken arch" level. The map is found in the lighthouse room, but you don't need it to use its secrets.

You need to rotate the view in midair to reach the second hidden platforms.

Alternative method:

In New Game+, Gomez can fly (press ↑↑↑↑ and jump), which is an easy way to descend from platforms.