Check out this amazing underground art museum in Frankfurt, Germany. What you see is an extension of the Städel Museum designed by Schneider + Schumacher. Not only do the 195 circular skylights offer natural lighting, they also create a beautiful and unique 'land art' to the landscaping above...
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But for their utility in the space below, the skylights were deployed to great aesthetic effect in the garden above. The circular windows dot the courtyard, including a sloping hill that serves as the domed roof of the gallery below. In addition to creating a visually striking space, however, the architects were intent on keeping it as a place for people to congregate.
"Before the museum was extended with our building, the garden was a public space to sit on--no fences, open 24 hours," one team member told me. "The students from the neighbor-building, the famous Staedel Art School, sit there during breaks, visitors rest there when having seen enough art, and children run around there." So they designed the skylights with foot traffic in mind--"you can even jump on the glass," the firm assured us.