Has anyone done this? is it possible by public transport? thank you!
I think you will have to drive. You can also double-check for bus options at http://www.visitnorway.com/us/getting-here-and-around/buses-and-coaches/.
Bus 930 from Bergen to Seljestad.
Bus 180 Haukeliekspressen from Seljestad to Seljord.
Local bus 301 from Seljord to Flatdal, but it only runs school days.
A taxi is an option (10-15 km).