That island has a ton of history packed into a really small area, so you definitely won't get bored. You can spend days just driving around the coast and checking out old architecture. For example, you can spend a morning walking around the fortifications in Valletta. After that, it makes sense to drive over toward Mdina to check out the old medieval streets. For some coastal views, the Dingli Cliffs are usually a solid choice. Also, you can head down to Marsaxlokk on a Sunday to see the traditional fishing boats.