Driving instructions are so oldschool.
Use your navigation on the mobile phone the city is big.
On A5 Departure is Darmstadt/Stadtmitte/Griesheim.
From Frankfurt train take S3 to station Darmstd hbf, 25 min walk to lokation.
Frankfurt airport is only about 40 km away from Darmstadt, so you definitely shoud try to fly there.
After landing at Frankfurt Airport just grab a train an go to Darmstadt train station (Hbf) or to Frankfurt train station and take a S-Bahn to Darmstdt Hbf.