What points of interest do you regret not having visited during your time overseas?

For me it was not visiting:
Easter Island - Chile (Command won't approve the 2 hour flight over)
Windsor Castle (Tour) - London (Didn't have enough time while we were in London.)
London Bridge - London (Same as above)
Blarney Stone - Northern Ireland (I as apart of the team that was in Ballyconnell in Ireland)
Taj Mahal - India (I had a chance to go but didn't take it.)

There are probably others but can't remember.

SGT Stewart, I've hit your list, you should make a return trip, there are some great things to see. That being said, I miss not seeing more of eastern Europe. I managed to get to Prague, Bucharest, Belgrade, and Dubrovnik. But missed Bulgaria, Macedonia, Israel, Egypt, and more of Turkey. We used cruises to hit a lot of the Mediterranean and Baltic Seas, and managed a fantastic rail trip through south and into central Africa.

The North/South Korean border. I had an opportunity to go and chose not to. I do regret that.