One of my players has the following power, which comes from Heroes of Shadow:
Ghost of the Rooftops Assassin Utility 6
At-Will (Special), Martial
Move Action, Personal
Effect: You climb or make a long jump, moving a number of squares up to your speed, without making an Athletics check.
Special: You can use this power only once per round.
There doesn't appear to be any limit on the difficulty of the climb. So, to take an extreme example, could this character climb up a polished crystal glass wall that is inclined backward without any equipment?
What about climbing along the ceiling like a fly... or spider?