I visited Hjo with my parents at easter 2008. It wasn't very far away from Mariestad, 1 1/2 h by bus i think, on the coast of the next lake - the other big one in Sweden, Vättern. Hjo is one of the best preserved wooden towns in Sweden and it was very interesting - despite of the cold wind and the only snowy time during whole my time in Sweden... It's an old spa town, but the old town itself seemed to be quite separate from it. In the end we found also an area with art nouveau villas, i guess they were more spa-related.