Dominating the skyline of Hamamatsu, ACT City is its tallest building by a good distance. On the 45th floor there's an observatory from which you can admire the city and surrounding scenery, from the ocean to the south to the mountains inland. Tickets cost ¥500 and are valid for the whole day, so you can go there in the morning for the panorama, then go back after dark in the evening to see the city lights.
I came to Japan from Manchester, England in 2003, and have travelled a lot since then, around Japan and in Asia. When I'm not working, I write satire and perform stand-up comedy in and around Tokyo. Check YouTube for a taste.