Europa Park, as previously mentioned, will be reopening from May 29th. It's been said they will max the daily capacity at 15,000, a quarter of their usual capacity (just for a fun comparison in park sizes, 15k is around Thorpe's capacity these days I believe...)
However, to book tickets you have to get in a virtual queue (similar to buying concert tickets and the like I guess). At time of writing, the virtual queue has over 28,000 people are is estimated to take an hour.
Will be interesting to see how it levels out in the future, and what this means for booking park visits in general over the next couple of months.