What is the best "side quest" published adventure?

[Oryan77]

What's the best published adventure you played as a side quest that lasted only a couple of sessions?

Please explain why it was so good. Did it have good NPC's, storyline, roleplaying opportunities, interesting encounters, ect?

 

[Crothian]

I did the Rod of 7 parts as a sidequest, but that lasted longer then a few adventures.

 

[diaglo]

S1 Tomb of Horrors

lasted all of 10 minutes total for the whole session.

we hit reset and played it again and it lasted a little longer the second time... (4hours) but still had a similar result.

edit: it included all of the above. great setting. great encounters. great stuff...