Not everyone will appreciate the humidity that comes with an indoor forest and turtle pond. But shoot... a Turtle Pond!! I don't want to be the sole naysayer, but I have to say... the lineups for the bathrooms are HUGE at peak times, so, uh, go at the hotel first.

If you find yourself at the Atocha station to change trains, maybe to head out of town for the day to Toledo or Segovia, make sure to get out of the gate and Metro areas and check out the old station. It is worth a little time. Also, outside across the street is some great architecture.