LONG BEFORE I even got there, the Rusenski Lom Nature Park seemed an enigmatic destination. A brief note in the guidebook had barely outlined the basics: The park consisted of a twisting series of gorges in northern Bulgaria, incised into a limestone plateau by one of the rivers that fed the Danube. But that was all I had to go on. I’d arrived in Ruse, an elegant Bulgarian city close to the Romanian border, with little to steer me beyond a vague impulse to find a place most visitors overlooked.
“I don’t know much about it,”...