When Amsterdam switched to Protestantism, a large number of monasteries and convents suddenly became useless. Most of these were converted to orphanages or hospitals, which remains their present function, while some have reverted to religious functions as the Dutch moved from rigidly Protestant to not caring about religion. A few of these complexes are quite famous, and I actually remember this one, which had a beautiful garden that's very inviting after a long night out and a long day of museum-hopping. Unfortunately I can't seem to locate its name, so it will just have to be the mystery building for now.