On my firsf night out in Kotor, I met a nice Australian couple who told me that they had booked a private one-way transfer to Mostar in Bosnia. I was quick to ask them if I could join, as I thought the driver would have to go back to Kotor in the evening. A visit to their agency and 50 euro poorer I was signed up for a day trip to Bosnia.
The driver went really fast, through winding roads but it still took us over four hours to reach Mostar. Once there I was told that I could spend one hour before the driver wanted to go back again, and to be honest that was enough.
Mostar is a really small city and is completely crowded with tourists. But that is also for a reason. The old bridge, called Stari Most that runs over the river Neretva is probably the most famous construction standing in the Balkans. It served as the border between the muslim land and the christian land, was blown up in the war and is now even used for people who jump from it. A cool place to be, even just for a good hour.