The population of Kardzhali is mixed. It is 50% Bulgarians and 50% Turkish. Both languages are spoken.
You can easily get to Kardzhali. It is recommended that you arrive in Kardzhali by bus, as there are buses from most of the major Bulgarian cities.
The region around Kardzhali has numerous ancient sites. Make sure to see the ancient city and fortress Perperikon, the temple and tomb at Tatul and the artificial astronomic cave near the village of Nenkovo. There isn't much to see in city of Kardzhali. Don't miss to visit the local history museum and Kardzhali dam.
Go to Kardzhali dam. It is very high (about 120 meters) and it looks marvellous.
Be sure to try their Turkish Biurek (Бюрек), which is something like Banitza. Of course there are many good restaurants offering good food. At least you can always go and eat a pizza.
In the dam lake there are also ship restaurants where customers can choose living fish for their meals.
There are several hotels in Kardzhali where you can stay at night. It is not expensive and the conditions are good.
Getting out is as easy as getting in Kardzhali. There are about 15 buses leaving to Sofia, especially in the morning, so getting out is not a thing to worry about.