wonder mail
No. Because it is hidden. The Pokemon do not know such a place.
24 floors
there are 15 floors in the hidden land.
in the hidden land but you are not able to recruit him there
No, Pokemon cannot be traded in or out of a Mystery Dungeon series game to any other game. However, Pokemon that evolve by trading can still evolve in Mystery Dungeon by using an item known as the link cable, which is found in the game. I know that this item can be found in Solar Cave in the older Mystery Dungeon games, in place of the Hidden Machines found in the locked chambers.
Go to the Hidden Land
there the "x-ray specs" and they reveal hidden stairs and items
Use Rock Smash
15f and 8f in the deepest part.
It doesn't have a limit. Even after you go into the Post - Ending, you will still be able to enter it.
There are 24 floors.
I think Lapras will come back to the beach area and you can talk to her to go, but I haven't played the game in a wile...