Love Hotel - Tokyo

You are correct in that they are not like other hotels where you call them up and make a reservation etc. Being discreet is the name of the game with them. Saturday night would be about the worst time of the week to try to get a room. If you have to go to one on a Saturday, then an afternoon would give you a better chance.
By nature they are meant to be affordable, although luxurious places do exist as well. For Tokyo the place to go would be Love Hotel Hill in Dogenzaka, near Shibuya. It's most easily accessed by exiting from the Exit #8 at the JR Shibuya Stn.
As far as tips go, the main one would be remembering that once you go in, you don't leave except to vacate the room. Some foods and drinks are provided in most, but are pricey, so bring whatever food/drinks/booze with you that you'll want for the time you are there. And don't forget your camera - take lot's of pictures. You'll still be chuckling at them decades from now.

Hi there,

Love hotels certainly are some of the most fascinating things of Japan, especially the history. Read Japanese Love Hotels: A Cultural History if you are want to know the fine details and get a good amount of recommendations as well.

They can be nearly found anywhere in Japan, in Tokyo Shibuya and Ikebukuro are the most famous areas and you can really miss finding them. Prices start at about 5,000yen per night, which is really good. However you do have to pay more if you want something more fancy or say a themed room. I would recommend checking in around 9 or so in the evening, this way you are before most other couples and can select your own room.