What it is
Rooftops of department stores and commercial buildings in city centers are said to commonly host seasonal beer gardens from around early summer (roughly Japan's early-May holidays) through the end of summer. The appeal is an open-air space for beer and light food, and these venues are said to be popular as an easy stop in the middle of the city.
Tips for enjoying it
Many beer gardens are said to run mainly on a time-limited all-you-can-drink plan, such as 90 or 120 minutes. Pricing, menus, and how each venue handles rain (a roof or not, cancellation policy) vary by location, so it helps to check the official website before you go. Popular venues can fill up on weekends, so booking ahead is recommended.
When to visit
Many venues are said to run seasonally from around May to September, though the exact dates vary by venue and year. If you have a specific venue in mind, checking its official website for the season's dates is recommended.
Some venues are said to promote their rooftop night views as a selling point. Some offer soft-drink or light-meal plans for families with children, though whether this is available varies by venue, so it's worth checking beforehand. Seating style — chairs versus standing areas — is said to vary by venue, and some let you request a preference when booking. Some venues are said to separate smoking and non-smoking areas, so it's worth asking about at the time of reservation if that matters to you.