Note:
If playing multiplayer.
Just break the glass until you fall into the cave.

Installing:

To download the map, just click on the MCedit link, and then you will get a zip file.
Unzip the zip file and open the folder.
Inside there should be abother folder called cave survival.
Put that folder inside .minecraft/saves.

Rules:
NO CHEATING!
No escaping to the surface until you have found the treasure.