This is an observatory spot named “Tenran Dai,” after Emperor Hirohito of the Showa era (Showa Tenno) who visited this observatory in 1981. One of the appealing point of this observatory, is that you can easily get there since it is adjacent to the Rokko Cable Station. (The last train leaves at 9:10 PM, as of 2017).

At the Tenran Observatory, there is also a restaurant where you can enjoy a night view. The dinner served here is in lower 1,000 yen range, which is reasonable for a restaurant where you can enjoy an exquisite night view.

It takes at least 40 minutes to get here from Sannomiya, by transferring on the bus and cable line. You can visit the official Rokkosan website for directions in English:
https://www.rokkosan.com/en/access/