This is a "garita" on the fort of El Morro. While it looks window-sized, it is large enough to stand in, and was used as a sentry tower.
Two of the pools at our hotel: one with a swim-up bar, a huge hot tub, and:
A pool filled with salt water, pumped in directly from the ocean (you can see it in the top of the pic). This pool was 6' deep all over, which struck me as odd until I realized how easy it was to float effortlessly in a calm pool of salt water.
We were told not to miss Friday night at this other hotel, the El San Juan, due to the live band, dancing, and incredible carved-wood interior. I was particularly impressed with the area around the pools in the back (theme?), but since it was dark and raining, this is the only one that came out.