Hi Korjik,
Thanks for your thoughts.
To answer your questions...
I made it plain as day that it was a pipe that carried waste water out of the mountain with significant pressure. They climbed up the mountain side and checked it for archers and traps...and found none
You are correct in saying that they did not know that the pipe was a dead end.
However, I disagree when you use the defense 'they did not know' and therefore were justifed in pursing that course of action.
Lets look at what they did know. They knew, for instance, that it would require a significant 3 - 5 hour journey up a mountain side, inside a cramped tunnel, crouching at half speed, in a pipe filled with 'gunk', where even if they did meet a 'nasty', they could not effectively fight or if they had their rope cut (which had the situation occurred, I would definately target), they would effectively fall to their deaths. Only one of the two had darkvision, so a lightsource was used.
More importantly though, in my opinion, is the fact that they willingly left three other party members without a care in the world as to what they do or what becomes of them. This was completely in their control (and had I been a player, I would of considered this completely selfish behaviour and unacceptable). They could of easily been killed in this fashion.
Btw, they roleplayed aprroximately 15 minutes exploring the pipe (I switch back and forth 3 times), although it did result in the party being seperated for half the game and the other three players fighting orcs alone.
Interestly, the other two players (which were in the pipe) believe they should also be awarded xp for the fight that the other three players were involved in. They believe it would be 'fair' and prevent uneven distribution on player xp.
I'd love to know your thoughts in this.