The Iskar is the only river that saws right through the Balkan range, and at Lakatnik it does it in style. On the eastern side of the gorge a wall of grey limestone rises almost straight up from the water, pocked with caves and streaked with lichen, and the railway, the road and the river squeeze side by side through the gap at its foot. Lakatnik itself is little more than a railway halt and a scattering of houses; the Lakatnik Rocks are the reason to stop, and on a summer weekend you will see climbers hanging off them like spiders.
The gorge has been a route for as long as there have been people here. Caves in these cliffs, Temnata Dupka among them, held some of the earliest traces of humans in the Balkans, and archaeologists have dug through tens of thousands of years of hearths and stone tools. Far later, in the late nineteenth century, engineers blasted the Sofia to Mezdra railway through the gorge with a string of tunnels and bridges, and for a long time the train was the only practical way through. The tunnels still punctuate the slopes, and watching a train slide out of the mountain beside you is part of the ride.
The road along the Iskar is a sequence of bends that follow the river's every whim, mostly medium-speed curves with the occasional tighter turn where the cliffs close in. There is not much room for error: rock on one side, river and rail on the other, and lorries using the gorge as the shortcut between Sofia and the north. The surface varies from good to tired, and fallen stones after rain are common. Mornings are best, when the low sun lights the western faces and traffic is lighter; on hot afternoons the gorge traps the heat like an oven.
There is very little at Lakatnik in the way of services, maybe a kiosk and a parking area by the rocks. Svoge, about ten kilometres upstream toward Sofia, is the nearest town and has fuel, shops and cafes, and it is known across Bulgaria for its chocolate factory. Downstream toward Mezdra, small villages offer roadside fish restaurants where trout comes straight from the river. Look up at the cliffs from the bridge before you ride on; the scale only really lands when you stop.