I am an American living in the Netherlands, and I recently converted my US PPL to an EASA PPL. I have significant night flying experience in the US, but I understand that night VFR in Europe is uncommon, and in fact only this year became authorized in NL. I know a flight plan in required, but I'm unsure whether I can file a plan with departure and destination the same, then just go fly around a bit and return at the specified time. Or must I have an actual route to a destination that I have to adhere to?
Yes you can file a flightplan with the same departure and destination. You generally do not need to include detailed routing, unless local rules require you to do so (but if you are planning to cross a country border, you probably need to include a point of crossing and estimated time). One thing to consider is that the EET in your flightplan should be accurate, since alerting service is based on that (if you don't arrive within a certain amount of minutes after your ETA, search and rescue efforts will be initiated). However, as long as you are contact with ATC while in the air, you can always just inform them of a revised ETA, and they can pass that on to your destination airfield.