There are many hotels in the city, including:
IBIS Hotel (0.60 km from the city center)
http://www.ibishotel.com/gb/hotel-2206-ibis-muenster-city/index.shtml
Mercure Hotel (0.55 km from the city center)
http://www.mercure.com/gb/hotel-5415-mercure-hotel-muenster-city/index.shtml
Agora Hotel (1km from the city center)
Cheap accommodation options include:
The Sleepstation Hostel : http://www.sleep-station.de/
The Jugend Gastehouse Aasee : http://www.djh-wl.de/jh/muenster/
There are also other options here at hotelms:
http://wwwuv2.uni-muenster.de/Formular/Leitfaden/hotelms.pdf
Parking
In front of the castle, on the Hindenburg place a sufficient number of pay parking for your car. If you stay in the city, we recommend the use of well-developed mass transit system or bicycles. By car you arrive at the short distances, often significantly slower. An overview of the route network of the local transport you can find here … At various points you can also rent bicycles, more information can be found at the Tourist Office: http://www.muenster.de/stadt/tourismus/radverleih.html