Wales is the new Ireland. While Cardiff may currently be winning in the coolness stakes, Swansea is catching up quick. Swansea is built in a smashing location, with a long promenade sweeping around Swansea Bay. The nightlife is concentrated around Wind Street, with a myriad of bars to suit all tastes, from the cheap-and-cheerful to the poncey-as-all-hell. Alternatively try the Mumble Mile, a pub crawl including 11 different haunts.
If you're in Wales, throw yourself, literally, into the outdoor pursuits.
Coasteering, climbing, abseiling and gorge scrambling are all superb fun alternatives to the standard stag do karting and clay shooting.