Although I usually wouldn't consider getting up well before the crack of dawn and driving up a mountain to be a part of a relaxing vacation, the effort is well worth it. Hottarakashi Onsen boasts lovely outdoor baths with gorgeous views of Kofu and Mt. Fuji. The best view, however, is at sunrise. The onsen opens early just for this, and also offers a breakfast service after the sun has risen.
There are a couple of important steps to having the best experience seeing the sunrise from your bath. First, check what time the sun rises. Second, get to the onsen way earlier. There are several buildings situated on an upper area, with stairs going down to the bathhouse. Bathers will line up above the stairs before dawn. Obviously the first ones in line get the first chance to choose where to sit in the bath, so they can pick out the prime spots. There's also the danger of missing the sunrise if you're too far back in the line - so be careful! Make sure to dress warmly if you go in the colder months. Waiting outside before dawn will be quite chilly! Tickets for the bath can be purchased from a vending machine. An adult ticket for unlimited bathing time is ¥800, but other tickets can be purchased to combine entry fee and towels.
When the bath officially opens (check the seasonal hours) you can head down the stairs to the bath. Hand your ticket to the person at the desk, and drop off your shoes in the locker. There are two outdoor baths on each gender's side. They are named Acchi-no-yu (that bath) and Kocchi-no-yu (this bath). Kocchi-no-yu is higher up on the hill, closer to the dressing room. It has a wooden rim that gives the bath a pleasant aroma. Acchi-no-yu is below Kocchi-no-yu, and is made with stones.
Once you find a nice spot, sit back and relax. You'll likely be waiting for a bit before the sun rises. The view is stunning, and it's incredible to watch the lights of Kofu slowly fade as bright rays of sunshine start peeking over the mountains. You can watch the snow on Mt. Fuji go from a dark purple, to bright pink, to brilliantly bright white.
After the sun has risen and you're finished bathing, you can exit the bath and go back up the stairs to the main area of the onsen. A small kitchen will have opened and be serving a traditional Japanese breakfast that you can enjoy while sitting outside and looking at Mt. Fuji.
The experience of being in an onsen and watching the sun rise over Mt. Fuji is incredible. Although many people come to enjoy the bath, the experience still feels calm and tranquil. Although it may seem tough, it's well worth the lost hours of sleep.