The short answer is that, for Europe, anywhere in the region can be the destination and anywhere else can be the stopover. You can also add an open-jaw in there so fly ICT-DEN-EWR-MUC-TIA, then get yourself to SPU and fly from there to BSL for the second stop and then fly home from there.
If you're really aggressive, you can also build in some long connections to add more destinations. Anything under 24 hours is just a connection so those don't count against your limits.
I flew ARN-IST over 4 days in January, visiting
Berlin,
Ljubljana and
Skopje along the way, all for 12,500 points as a one-way Europe award. I had 20ish hours or more in each city. It was awesome. I spent a
couple nights in Istanbul and then headed back home.
Oh, and my return was IST-MUC-EWR, with a cool 23:55 on the ground in MUC.
