Ok. Here is how the plan works.
Land in Sofia
1 day later SEPULTURA concert
1 day later start a week long mountain hiking trip with sleeping bags and tents and whatnot
Stay at over 2500 altitude and have 12-14 hour day long walking trips. Keep in mind you will never sleep twice in the same place; so everyday you walk, you have to walk until you reach next stop to sleep. Turning back is not an option.
1 day after we return from the mountain trip there is a possible 100km bike ride around vitosha mountain.
1 day later IRON MAIDEN concert... will be another blast.

After that we have 1-2 free days. Will check possibility to rent a car and visit one of these places.
RILA MONASTERY
PERPERIKON
PLOVDIV
And then there is a TORI AMOS concert at NDK
after one day rest we return to work. (downer)