Humanist ceremonies (we call them ceremonies rather than services) can be very traditional. Sometimes they're even held in churches, although generally, like Melrose Abbey or Mansfield Traquair, they are 'decommissioned' ones. But generally they take place in castles and hotels, village halls and nightclubs, on farms and in stables, up hills, on beaches, in people's living rooms and back gardens. Anywhere 'safe & dignified' as the Registrar requires.
The really good news is that you don't need to get a licence for the venue: because the celebrant is licensed, we can conduct your wedding pretty much anywhere.