MarkB
Legend
Interesting that this part of the OP hasn't been addressed so much.
I'm wondering if the players didn't try to climb because there was no 'Climb' skill listed on their character sheets?
Alternatively, in a narrative/cinematic game, it isn't obvious that ALL epic heroes can climb 200 foot walls. That's more a mechanical artifact of D&D rules. Maybe they reasonably assumed that only epic thieves can climb anything. If so, it's not their fault that there's a discrepancy between what the players assume the PCs can do vs what the PCs would know they could do. In which case, I'd allow a Wisdom check to clue them in.
One of the keys to Epic play is presenting Epic challenges. If the tower is climbable by even an untrained Epic character, clue them in during the description - i.e. "the walls, though sheer, would present little obstacle to practised adventurers such as yourselves".
If, on the other hand, it is a tower built to withstand assault by Epic creatures, then maybe those walls shouldn't be easily climbable - either they're built ultra-smooth and tough to grant no purchase, or there are defensive measures built in to discourage climbers, or maybe they're not physical walls at all, but planes of force that repel anything which touches them.