Finding the Raufarholshellir Lava Tube

Any help in finding the entrance to this lava tube that passes under road 39 southwest of Hveragerdi? Someone else you couldn't find it without a gps and I will not have one of those.

Thanks.

I have this point on the free gps map http://www.ourfootprints.de/gps/mapsource-island_e.html</a>
N63 56.340 W21 23.785

One Km. north of junction 38/39/42, on the east side of the road. Signed.
B-)