Kotor is a compact medieval city — the entire UNESCO-listed Old Town is about 1.4 km end to end — but it punches far above its size. Inside the walls you have a fortress that is one of the best viewpoints in the Mediterranean, a 12th-century Romanesque cathedral, a world-class maritime museum, and the famous free-roaming cats. Outside the walls, you have a 28-km UNESCO bay that is best seen by speedboat, a cable car to a mountain 1,348 metres above sea level, and day-trip access to baroque towns, volcanic-blue lakes and Europe's deepest canyon.
Most visitors come on a cruise and have a single day. That is enough for the Old Town and the fortress — or the Old Town and a boat tour. It is not enough for both. Two full days covers everything in Kotor properly; three days lets you add an inland day trip. The single activity that most visitors say they remember longest is the Blue Cave speedboat tour: three hours that link four of the bay's water-access highlights in a single morning.