Bats can go relatively invisibly throughout the city unless you know that they are there. The bats in Amsterdam are very small and can easily be mistaken for birds by the untrained eye.
The province of North Holland has some of the best resourced bat experts in the world. I was lucky enough to meet one of them with Natuur je Beste Buur, the environmental group I volunteer for. It was incredibly fun and educational. We went for a walk around the sports parks and spotted several bats flying around.
We learned a lot in one evening, too much to share everything, but I will share as much as I can.
Once we knew what to look for, we spotted 3 bats flying around our tiny little garden just a few nights later
There may bat houses that you can purchase in your local area. Do your research to ensure you have the best home for the bats that live near you.
If you are interested in knowing more about building a bat house you can watch this US based video
There are also many resources in English available to help you on this Dutch site: