Rooms are held back at the DESY Hostel until 23 November 2018. Please mention the keyword FF Meeting" on their 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 13 November 2018. Please mention the keyword "DESY, FF Meeting" 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: