Based on your 2.5 hour session reqs... I think I can think of a pretty solid 6-8 session venture that not too many folks know about.That one would be pretty stout for the sub-20 crowd though. As for the request format... just put it in as the 'great traverse'.
Please note Format item #1 that there can be multiple sessions for one dungeon. You then start where you left off the previous time.