• Museum opens on event days only, since the free exhibition keeps the observatory's event times, so check the calendar before you go
• Family ticket at the desk: 2 adults and 3 kids for €31.50, sold only at the ticket office, not in the online shop
• Step-free museum and Einstein Hall, but the building is a listed monument and some areas are not yet wheelchair accessible

Germany's oldest and largest public observatory, open since 1896 in the middle of Treptower Park. Its centerpiece is the Great Refractor, nicknamed the "sky cannon": at 21 meters and 130 tons, the longest movable refracting telescope in the world, and still working.

Inside are a museum of astronomy from Stonehenge to space telescopes, a giant iron meteorite, a 31-seat planetarium and the hall where Einstein lectured on relativity in 1915.