There is a lot of interest in proposing to their girlfriend on the Harder Kulm, Interlaken. You can either walk up the signposted trail or use the furnicular railway to get to the restaurant. It has a viewing platform at 1,322 metres above sea level, where you can look down on Interlaken and Lake Brienz and Lake Thun. There is also a spectacular view of Eiger, Mönch, and Jungfrau mountains (on a clear day).
I have visited the Harder Kulm restaurant on several occasions. The picture was taken on the 17th June, 2017, at 17:36:33. It shows you the location of the sun. The picture also shows some building work. An extension to the restaurant. It is possible to be legally married in the restaurant. I believe the authorities make the journey up from Interlaken at least once a month during the summer to perform the ceremony.
Does it get crowded? Yes, at certain times. It will be busy on hot, sunny days; the weekends; and when there are several marriage ceremonies. You will need to do a search online to find out the dates of the marriage ceremonies. There are Asian tourist groups visiting the viewing platform. They never seem to go into the restaurant or hang around for long. The furnicular railway only operates to a timetable. There will be times when the viewing platform is almost empty.
Check out my pictures from the surprise wedding proposal with Mike and Kate: https://johnspixs.com/wedding-proposal-on-the-harder-kulm/. This happened at 10 a.m. and between visiting tourist groups.