Night of Museums in Bern, March 22, 2013
Stalactite cave of Bern
Since 2003 every year in March some institutions in Bern opens their doors for a night and show their interior to the public. First it has started only with museums (that's because it's called "Night of Museums"), but then also other institutions like banks, hotels, parliament building, townhall, and different services joined the event. All the buildings that are involved, are illuminated, so you'll find it easily.
=> Museumsnacht Bern, Fr. 22.03.2013