The name comes from an observatory. Tenmonkan is named after the Meijikan, an observatory and calendar-making institution built by Shimazu Shigehide in 1779, and the district that now carries the name is a block where several arcades cross one another. Bunka-dōri, Yamanokuchi Hondōri and the streets around them hold restaurants and clothing shops in considerable quantity, and the arcades meet at angles rather than in a tidy grid.

Black pork tonkatsu, ramen, cafés, souvenir shops, izakaya and bars are all here, and there are alleys inside the block still fitted out in the manner of a row of street stalls, narrow enough that two people cannot easily pass. Trams connect the district to the rest of the city, hospitals and schools are close by, and Tenmonkan therefore functions as a place people live beside as much as a place they come into for an evening out. Ash from Sakurajima falls regularly on the city, and on ash days the difference between a covered street and an open one becomes immediately obvious underfoot and in the air.

It is slightly odd for an entertainment district to be named after an observatory. A block that grew into the centre of a city's nightlife has inherited the name of a building where the calendar was calculated, so there are two hundred years of divergence between the name and its contents. Place names behave like this more often than not, and rarely get corrected. They keep the name of whatever was most conspicuous on the site first, long after the thing itself has gone and everybody has forgotten what the word originally referred to.