Kep
I am honestly a bit torn on whether to recommend Kep. We combined it with Phnom Penh over a long weekend, which worked pretty well. To get there we took a bus (booked via our hotel in Phnom Penh) which worked fine but took forever, so that on the way back we decided to get a taxi instead (again organized via the hotel), which cost around USD 60 in total and was absolutely worth it for us.
The reason I am torn is that Kep feels much more local and authentic than many other places and gives you a glimpse of what feels like the "real" Cambodia. On the other hand, the beach is honestly nothing special compared to many others in Southeast Asia, and unfortunately we also cannot really recommend the hotel we stayed at, the Saravoan-Kep hotel. I feel a bit bad saying this because the rooms actually looked nice, the staff was super friendly, and especially the restaurant is very cute with a beautiful view over the sea. But let's just say there were definitely animals in the walls, and at night they were definitely not quiet.
We also went to Koh Tonsay (Rabbit Island). Again, I would not necessarily recommend going for the beach itself, but if you are up for a bit of an adventure, it is a fun experience. You can simply ask for a boat at the Kep Koh Tonsay Tourism Port (bring cash). You can simply ask at the Kep Koh Tonsay Tourism Port, bring cash, and they will organize everything. It all feels a little sketchy at first, and the boats look like they are from the previous century, but everything worked perfectly, including the pickup at the agreed time. The biggest surprise was actually the food on the island. We unfortunately do not remember the name of the place, but it had blue sunbeds, and the lovely lady running it took amazing care of us.
Location: Kep, , Cambodia