Rooms can be booked at DESY Hostel. Please fill in the registration form: https://welcome-services.desy.de/e17/req1/index_eng.html
A limited number of rooms are held back in the Mercure Hotel am Volkspark until 4 November 2019. Please mention the keyword "DESY" when booking a room, using the following e-mail address: H1659-RE1@accor.com ; only then you will be eligible for the DESY rates.
Google Maps link to the Weihnachtsmarktstand: