Here there is a list of different coworking places in Rotterdam where you can rent a flex desk and go to work.
Startdock
Flexible desk from 8:00 am - 6:00 pm for 69€ month.
Spaces
Open every day for 100€ month.
HNK
From 8:00 - 18:00 for 15€ per day.
The student hotel
Open every day, its also a hotel. For 99€ you can get access to the coworking, lobby, restaurant and gym.
The progress bar
A coworking located in the island that looks like a fork. For 119€ you can get a month subscription.
42workspace
Coworking from 125€ per month.