Hotel Seven Days
https://sevendays-hotel.de/en/karlsruhe
About 80 € per night, a 20-minute walk to the conference venue
https://maps.app.goo.gl/BUis8obQK2MTZCuv6
Hotel am Karlstor
https://www.hotel-am-karlstor-karlsruhe.de
About 70 € per night, a 30-minute walk to the conference venue
https://maps.app.goo.gl/gvLybpaTtH1kZm5i8
Hotel Erbprinzenhof
https://www.booking.com/hotel/de/erbprinzenhof.en-gb.html
About €85 per night, a 25-minute walk to the conference venue
https://maps.app.goo.gl/ZQ9REGSHcTLrLVXR7
Leonardo Hotel
https://www.leonardo-hotels.com/karlsruhe
About 100 € per night, 15 minutes by metro
https://maps.app.goo.gl/MWP4yNLvNcc1oVnv7
B&B Hotel
https://www.hotel-bb.com/en/hotel/karlsruhe
About 80 € per night, 20 minutes by metro
https://maps.app.goo.gl/xSsTVGU1nmK3qwRR7
Hotel Barbarossa
https://www.hotel-barbarossa-karlsruhe.de/index_en.html
About 90 € per night, 15 minutes by metro
https://maps.app.goo.gl/bRMmUEGuEc9HC9Ez9
In addition, there are many apartments and Airbnbs available.