As any salaryman knows, there are sometime occasions when you miss the last train home and are stranded in Tokyo for the night. If it does happen, you're not doomed to a night wandering the streets or fighting off sleep in a bar or cafe. There are a number of capsule hotels across the city, and if it's Roppongi that you're stuck in, Vivi Capsule and Spa is centrally located and reasonably priced. If you choose to stay for sightseeing, the location is hard to beat; it's within walking distance of two subway stations, more shops and restaurants than you can wave a stick at, attractions such as Tokyo Tower, the Mori Art Museum and the National Art Center, and interesting nightlife venues like SuperDeluxe and, in the same building as the hotel, The Pink Cow.
Depending on the level of comfort and isolation you want, there are three choices of places to sleep, costing from roughly ¥4000 to ¥4800 a night. For effortless heavy sleepers, a reclining massage chair in an open room might be an option, if you don't mind a bit of light and people walking back and forth nearby. Slightly more conducive to sleep are the bunks, essentially a glorified wine-rack for people; I wouldn't really recommend this for light sleepers, because you're separated from your neighbors only by curtains, and their snoring, snuffling and shuffling adds to the muffled dancefloor beats from the nightclub on the next floor. The best place is the capsules; in a separate room, these are quiet, cosy and comfortable, and definitely worth the extra few hundred yen.
There are plenty of other facilities on offer. The 'Spa' part of the name refers to a hot stone spa, which I unfortunately didn't have time to try, but I did get to enjoy the sauna (complete with built-in TV), the big hot bath and, wanting to do my sauna in authentic Finnish style, the cold bath, for a good ten seconds. Elsewhere, there's a small lounge where you can buy snacks and light meals and sit watching TV, a massage salon, a small fitness room, and vending machines for soft drinks and alcohol. You get a (very narrow) locker to put your things in, and towels and nightwear are provided, though there's a small fee for storing larger luggage.
Like all capsule hotels, it's not intended for long stays and isn't a luxurious place to stay; but it's perfectly clean and safe, and for the price you pay the facilities, comfort and location make it excellent value.