Equipment for your level.
The backstory. Your group has been secretly following a caravan. Thrane believes that the caravan is transporting coffins containing old, powerfull undead. When the caravan was nearing the karrnathi border a part of your team halted the caravan.The plan was to use mind-magic to convince the caravan-guards to hand over the boxes. The plan failed miserably. Only two common soldiers survived. they spoke of an airship interfering and taking away the cargo. You followed and scouted the terrain. The enemie is locked up in an old border-tower. It's four floors high (about 30'). The entrance can be sealed with a stout wooden door and a portculis. There are arrow slits all around the tower. It is open to the air, and from the top of the tower is an airshipramp.
the mission :
1. End the threat to Thrane. It would be best if you could obtain all the crates, one way or the other. If that is impossible, destroy them all. Under no circumstance should the undead be released.
2. Get more information. Try to take a prisoner.
3. Make sure info gets back to Thrane.
This is not a suicide mission. While some of you might be zealots, some should try to get out alive with some info.
This is an experiment for me as a DM. It could turn into a campaign with one group of players chasing another group. If any of your characters survive I might use them as recurring nemesisses, if they gety whiped but it proves to be an interresting fight I might do this more often