I traveled Serbia by bicycle as part of my eastern Europe cycling tour. I spent a few days in Belgrade and was really impressed. I honestly didn’t expect it to be as cool as it was. The communist-era architecture and the vibe were pretty fun. I then cycled along the Danube River to Romania 4-5 days. I mostly camped along the way, but one night I was the lone occupant in a hotel/restaurant  that had opened just for me when a ferry was canceled due to weather. I did one great summit hike overlooking the Danube in a national park, which I later found was closed to people without a guide, and a bear came into my camp that same night. Overall Serbia turned out to be a great adventure.