By public transport, the easiest ways to the Rila Mountains are through Rila village (for the monastery and surrounding hiking trails) or Samokov (to reach Borovets ski resort). Buses to Rila leave from Sofia's Ovcha Kupel bus station (22 lv, two hours). For Samokov, board a bus from Sofia (6 lv, 1¾ hours, hourly) or Plovdiv (7 lv, two hours, four daily); from here you can take a minibus to Borovets (1.30 lv, 20 minutes, hourly).
Roads to both Rila village and Borovets are well maintained. Those beyond these primary tourist draws tend to be potholed and with plenty of sharp bends.