Hope this information overload is usefull haha:
Always summer
Sapporo 2018 and 2019 - Both times when I took it in Sapporo it was at the same university campus / high school… The buildings were on the older side. Large rooms probably 80 people per room (maybe even more). Its was fine but on the humid side and a bit difficult when its soo hot haha
Its the last stop on the southern line of the underground and there is a dedicated bus which then takes you to the campus (2 minute ride maybe, its short). The whole trip could be 1 hour and a half from central Sapporo.
I timed it a bit too good the second time when I went there. I arrived to the station to take the last bus (me and another guy haha). The test started 30 seconds after I sat on my seat . haha
Nagoya - I am aware of two potential locations for the exam
One righ next to Nagoya JR station. This is where I went this July. Its a new-ish building, really nice inside and comfortable (as there are air cons constantly working lol). The first few floors are a shopping centre / department store which makes it a bit confusing. There are lifts to the higher floors where the exam rooms are. I think it was some kind of conference centre / business place.
The other location is maybe 1 hour from Nagoya JR station by underground. An university. People said that its fine there too, a bit on the older side. Some people who took N1 and N5 went there.