El Retiro is a magical place to get lost in if you want to surround yourself in the tranquility of nature. However, the park is so damn big, you'll need more than one trip and possibly a map to navigate through it all, which is why I pick specifically the "Palacio de Cristal."It's essentially a green house, but if you let your imagination run wild, it can be so much more than that. I've sat there for hours gazing at the sun and clouds pass me by. If that sounds boring, then get one of the best photos ops inside the palace because the lighting will never fail you, and then begin the adventures that are awaiting outside.Caves to walk through or climb on top of, steps to sit on in front of a massive lake and spans of shaded grass make for the perfect place to picnic, people watch, have a yoga sesh.. whatever it is that brings you inner-peace. During the summer months, there have always been free art exhibitions inside the crystal palace.