On my last day alone in Madrid, after all my friends had dispersed back to their respective homes and extended adventures, I wandered through Retiro Park.

There I found El Palacio de Cristal. This building of almost entirely steel and glass is a whimsical and airy building planted in the foliage of the park. It was originally built in 1887 to hold exotic plants and now houses temporary exhibits.

The exhibit on display in this utilizes your imagination and the surrounding trees to create an artistic space. The different colored circles come in pairs and are meant to create an illusion of columns that represent the tall trees outside the building.