The new Terminal 2 at Sofia airport, which hosts the major airlines, has a multi-story car park where many of the hire cars will be parked. The old Terminal 1, which the low-cost airlines use, is more cosy and the car park is just outside the terminal. Your hire company should give you a map and directions of which way to head.
Leave the car park and follow the road round towards the airport exit. You will join the airport link road which is a dual carriageway. Stay on this road - do NOT take the exit for Sofia centre. The road goes through a suburb and then bears left and joints another dual carriageway (this road seems unfinished to your left). At the end of this fairly straight road, bear right on to a link to the main outer ring road for the city. Take this road right (It starts as Route 18 and changes to Route 1)
After about 11.5 kilometres you will reach a major junction with cobble stones and tram lines.
Turn left (E871) leading to KULATA - which is on the Greek border (Route 1 turns left here too).
After about 15 Km take the slip road signposted Kulata and E79.
Continue on this highway until you reach Simitli - about 90 Km. Then take the slip road to the right towards Bansko (41Km).
When you reach Bansko bear right just before the river and follow this road parallel to the river and then across the river to traffic lights. Turn right. After one kilometre the road bears left. Take the small road to the left. There is a sign for Mountain Dream here. Mountain Dream is straight ahead of you. Enter by the small drive to the left of the first building.
Depending on your speed and the traffic the journey will take between 2 and -2.5 hours.
A longer, prettier and less stressful route is as follows:
Take the road out of the airport. When you reach the junction with the main road into Sofia do not take the turn towards the city centre but go under this dual carriageway main road and take the slip road to the right (I can't remember where it is signed to but it looks as though you are going on an ordinary road heading towards the centre but after 100m part of the road bears right and feeds on to the main road heading out of Sofia.
Take the first exit (if you do as we did and take an industrial exit don't worry it leads on to the correct road.) The exit is not particularly well sign posted but goes down a fairly sharp incline. That is the end of the difficult bit. Now just go straight, through the outskirts of Sofia and along a winding but generally good road through attractive scenery. Just before Samokov take a right towards Dupnica (along a bypass to Samokov). At Dupnica join (a left turn via a slip road on the right) the Route 1 (E79). At Simitli take the signed route to Bansko via a slip road.
Driven this route by transfer taxis it will take about 2.5 hours. We allow at least 3.5 hours.
NB Take care on the roads. Potholes of varying depths are frequent and unexpected. Most hire car insurances will not pay up for pothole damage. In comparison to England some Bulgarian drivers are scary and take far greater risks. Keep your wits about you. The speed limit on the E79 is 90 Km unless otherwise shown even though the road is often dual carriageway. The police use mobile radar speed traps to supplement the permanent ones on this road.