In addition to the Portman, the Purple Mountain comes to mind, but that place might as well be on Mars. In any event, the Portman's pool is really nice. I used to be a member of their gym (barter deal), but now I can only avail of the their facilities when I have guests staying there; I'll be sure to let you know the next time an opportunity knocks.

I'd also be surprised if one or more of the newer hotels in town doesn't have an outdoor pool.

In any case, if anyone can think of a nicer outdoor hotel pool than the Portman's, I want to know about it.