This could be the idea for you!
A great way to experience the wonders of the Highlands is to hike from Skogar to Thorsmork in one day, and take the evening Bus from Thorsmork to Skogar after a beautiful days walk. You could have an early start (if you are driving from Reykjavik you should start no later than 07.00) and hike your way along the Fimmvorduhals trail to Thorsmork in 8-12 hours. If you have a car parked at Skogar you could even reach the evening bus back to Skogar.
A later start from Skogar provides a afternoon and evening hike along the Fimmvorduhals trail, with possibility to camp on the way, or perhaps at the Fimmvorduskali mountain hut, standing at the highest point of Fimmvorduhals. The following day your hike continues to Basar in Thorsmork, passing the eruption site of the volcanic eruption in 2010. In Thorsmork you can stay for a night on the camping site, in one of the mountain huts – or perhaps continue by bus to your next destination.
The distance between Skogar and Thorsmork (Basar) is about 25 km. Hikers en route across The Fimmvorduhals Pass to Skogar can divide the leg by staying overnight in the Fimmvorduhals hut in the pass after a 5 hour walk and continue for five hours the next day down to Skogar or visa versa. The Fimmvörðuháls pass from Skógar to Thorsmork is one of Iceland’s most popular hiking routes. The trail starts at Skógar, along Skógá River and past its many waterfalls, including Skogarfoss. The trail continues up between the two glaciers, Eyjafjallajokull and Mýrdalsjökull, to the recently formed lava and the new craters, Magni and Móði. Here the fresh lava is still steaming under the surface and the heat of the lava can still be felt. The trail then heads down from the craters to the magnificent Thorsmork glacier valley, continuing along beautiful geological features and amazing views over the highlands of Iceland and the surrounding glaciers.
This hike is demanding and some effort and certain endurance is required. The elevation of over 1000 m (3280 ft) and total distance of 25 km (15.5 mi) that will take 8 – 12 hours to cover. Good health and some hiking experience is required. The Fimmvorduhals hike is a once in a lifetime experience for all hikers and nature enthusiasts! This trail is open from mid June to Mid September. (source: re.is and nat.is).
You can also get experience guide for this travel.