This video says about itself:
I put a swift nest box up this year, which was completely ignored until today.
On the medieval Hooglandse Kerk church, there is artificial nesting opportunity for these birds. Swifts are flying around. Close to the church, there is an antique shop in a building from the sixteenth century. The owner has taken various measures to help the birds nest.
As we walk to the castle, a greenfinch sings in a treetop.
Most swifts in Leiden nest near the old harbour.
There is a swift nest above the praline shop as well.