Weekend break for 21 year old son

[Marchintospring]

My DS is turning 21 and I'd like to get him and his girlfriend a weekend away for his birthday.
Somewhere Midlands or north ideally. He doesn't have a car at the moment so it needs to be city based really.
Any one knows anywhere suitably quirky or romantic for the youth to stay or visit?

Ask him.
What would he like?

Or get him a voucher for a hotel chain so he can choose himself like hyatt or hilton

Whitby
Belfast

Liverpool? Easy to get to on the train, near the sea and great nightlife

York

Is Durham too far away? I haven't been for many years, but I love it for a wander round. I think some of Harry Potter was filmed at Durham Castle. The cathedral is gorgeous and peaceful, of that's his bag. Loads of cobbled twisty streets to explore and quaint shops.

He says he doesn't want anything.
He spends all his time with his girlfriend and they do like going places together.

A voucher would be perfect.
He's done Liverpool and York I think. Durham and Belfast are great ideas but I don't see how I could make it a gift unless there's a specific hotel. Maybe a chain voucher is a solution.