what is wrong with wiath and what happens if the horse gets on top of a hole and it cannot escape?

Horses cannot climb ladders.

If a horse falls into a hole big enough to hold him with room to move, he might be able to jump out if it's not too deep.  While horses usually jump on the run, they can jump from a standstill as well. 

They don't have to get their whole body out at once.  I've seen plenty try to jump out of their stalls over doors that they could get just their heads and front legs over, then push and heave with their backs and hind legs and scrabble their way out.  Presumably a horse could do the same with a hole.

If a horse gets in a deeper hole, they usually dig out around the hole to make a ramp for the horse to come up.  If that's impossible, they'll have to be hauled out with heavy equipment like a crane or helicopter.