Kjustendil is a city in Bulgaria. Around 45.000 people live here.
The Ring Road
Kjustendil has a sort-of ring road. If your driver is going to Kjustendil and you're not, it is an option to take this ring road. Since the border crossing to Macedonia is very small and the only reason to go further west after Kjustendil, traffic is very scarce and people are reluctant to stop for you as this road passes through a gypsy neighborhood and the people here are not very fond of the gypsies. You most probably will succeed in passing Kjustendil this way but it will take you a long time. It might be a better idea to ask your driver to drop you off at the western part of the city or walk half an hour from the city center to the West to where the local road meets the highway again.