you can ahve day trips to Sofia, Plovdiv, Melnik and the Rila Monastery the last one together and beautiful with a wine tasting in Melnik.
Or you make individual a trip to Sofia via Bus or have a look to Samokov, visit the Bronce smith, eating in the Starata kaschta, walking to the Bazar try some good cheese and buy some wine...
I was wondering if it was possible to take a day trip fom Borvets to one of the other ski resorts in Bulgaria such as Bansko or Pamporovo or one of the others?