There are several options within a 5 to 10 minute walk from the Postillion Convention Centre WTC Rotterdam.
You can find the hotels recommended by the Postillion Convention Centre WTC, that provide special rates for RIPE 79 attendees, via the RIPE 79 Hotel Booking link.
Alternative hotel options can be found via travel sites like booking.com, hotels.com, airbnb.com or through travel agents.