The word "rotunde" (or rotunda) refers to a building that has been build in the shape of a cylinder or barrel. Normally, you will see a dome or cupola on top of the rotunde. The Pantheon in Rome can be categorised as one.
It is also possible to see "rotunder" in Denmark. For instance, if you take a trip to the island Bornholm, you will be able to see four of the so-called "rundkirker" (churches). These specific types of churches was build during the medieval period, and there are only seven preserved "rundkirker" in all of Denmark.
With beautiful nature and a lot of history, Bornholm is definitely a good place to visit!