During the August vacation from work, I picked up a new hobby. Simply put, the idea is to go into any random hotel in the city with an extremely nice pool, preferably on a higher floor with a nice view of the city, act like you are staying there, and steal time in the recreation area.
The first successful attempt was at the AC Hotel in Barcelona, at the Forum. The pool is on the 13th floor underneath a big cantilevered chunk of the building. It has an amazing view of just about everything you could want to see in Barcelona. You can even see the top of the Herzog and DeMeuron triangle. It's full of water again, and seagull poop, again.
Anyways, no one said anything to us the entire time we were up there, in the jacuzzis, the saunas, the outside pool, etc... I even went back a second time a few weeks later, and there wasn't a soul in sight.
The next attempt was the Hotel Diagonal at the foot of the Agbar Tower. Don't be fooled by this hotel. The roof is incredibly lame. not only is it only 9 or 10 stories high, but the pool is about the size of two of the three jacuzzis from the AC hotel. It's worth going up to the top, but don't bring your swimsuit.