This volcanic crater, 30km north of Bandung, has a flat, elongated summit that resembles an upturned boat (prahu). It's a huge attraction and certainly a spectacular sight, but also a major tourist trap. If you do decide to go, try to aim for early in the day as by noon the mist starts to roll in. Expect forceful guides trying to sell you overpriced souvenirs. Many foreign visitors find it pricey and not worth the hassle.
It's possible to circumnavigate most of the caldera on foot, but as wannabe guides can be aggressive and tourists have been robbed, there are better places for a highland walk.