Berlin - 1st of May
I arrived the same time a few years ago and yes, things were open. Do Turkish restaurants ever close? Maybe not everything, but you will be able to eat. And train stations never close so that is always a good bet and often can be a very good choices as well for eats, if not for dining.
It was a lovely time to be there - chestnut trees in full blossom. If you can take the original city walking tour, the guy will direct you to some special local restaurants and beer stubes.