Sports fan? It's the perfect entree for a solo traveler. Perhaps you play a sport. Perhaps you're a big fan of a sport. Either way, it's something you have in common with a large group of people in other countries.
Sports bring travelers and locals together in several ways, according to a post in Vagabondish, a Web travelzine. You can learn about a new sport in a foreign country; you can join locals playing casually; and you can visit during a big sports competition.
When I was in Spain (see post) last June, I ended up by accident in a small restaurant in Barco de Avila during the final match of the country's soccer league. It was Real Madrid against...another team. (Maybe you soccer/football fans remember). Well, this place was hopping!