I visited Yokohama on a recent trip to Tokyo. This being the 2nd largest city in Japan it’s said to be a mini Tokyo so I’m not sure if I would put this on a must visit list since it’s so close to Tokyo itself. None the less it’s worth a day trip (or half day) if you’re going for a few specific things like the Ramen Museum. It’s only about 20-30 min from Tokyo by train.