Groupon have released a new deal today which is giving users a serious discount on the Harry Potter tour in London. The tour itself normally costs £33, but with this deal you're getting butterbeer, souvenir and get to see Special Guests.
The only draw back with this is that there are only specific dates, so if you're travelling from outside of the UK it may be a bit more difficult. However flights are pretty cheap and you could hop over to London for 1 night just for the tour and have a nice meal out. You could even stay in the Harry Potter hotel to top things off for your magical experience.