In the Retiro Park there is a building that stands out for its resemblance to a greenhouse, in fact it was. The Glass Palace was built on the occasion of the Exposición de Flora de las Islas Filipinas. It was used as a greenhouse for tropical plants and at the same time an artificial pond was created right in front of it.
The Glass Palace is much more than a glass structure. It has had different important roles: it has hosted Exposición Nacional de las Bellas Artes and currently it is one of the exhibition centres of the Reina Sofía Museum. From November 16th to March 3rd you can see there the sculptures as a part of "Invisibles" a work by Jaume Plensa. This work consists of three pieces that are an allegory of the silence necessary to see what is apparently invisible. The intention of these sculptures is to ask for silence at a time when the artist considers that there is so much noise.
If you visit El Retiro do not forget to go to the Crystal Palace and visit everything it offers inside and outside.
Related stops: Stop no. 2 of route 1: Historical Madrid, stop no.13 of route 2: Modern Madrid (Puerta de Alcalá).