International Summer School, Regensburg, Germany, 2023
Public transport planners: bahn.de (Deutsche Bahn), RVV (local public transport)
Contribute to/formalize math in your favourite proof assistant :)
Visit Kloster Weltenburg: basic information on how to reach it
Visit Walhalla (the building, not the mythical place) Wikipedia entry
Take a boat trip on the Danube
Take a trip to Munich. Beware: The Oktoberfest is ongoing, with the obvious advantages and disadvantages (the Oktoberfest is a crowded affair and also public transport to/in Munich will be crowded).
Go climbing. There are two indoor climbing options: Boulderwelt (bouldering); DAV Kletterzentrum (rope-climbing; requires prior climbing experience)
Take a closer look at the medieval city centre of Regensburg: Dom (cathedral), steinerne Brücke (stone bridge), Rathaus (town hall), Schloss Thurn und Taxis, …
Visit a museum, e.g., Haus der bayerischen Geschichte
Take a trip to Nuremberg
Visit the (small but nice) botanical garden on the university campus
Explore the river Regen by canoe
Play Ultimate Frisbee on Fri afternoon (ask Matthias Uschold about the details): coordinates: time: September 22, 17:10; location (on the university campus): Google Maps, GPS: 48.999590, 12.095264.
Take a hike; the usual websites provide routes, e.g., komoot