
There are a few (!) single rooms available at Van der Valk Hotel Leiden (Haagsche Schouw), single room 75 euro + 10 euro breakfast (not a block reservation). There are also still a few rooms available at the Bastion Hotel Oegstgeest.
These three hotels are within walking distance of Leiden Observatory (or easy by bus).
** Note that these hotels may fill up fast, so book early! **
Other options are: