As there is no room in our bathroom to fit in a wallmounted towel rack I bought a three-way towel rack that could be hung at the back of our bathroom door. Unfortunately the space behind our door was not big enough to fit it in. So we decided to rebuild a smaller hanging towel rack with a little help of IKEA parts.

Materials:
3 GRUNDTAL rails, 2 fittings for mounting over the door top from GRUNDTAL door hanger, 2,5 m shelf studs, natural wood wax, a saw, sandpaper and screws.
First of all we build a frame out of the shelf studs. Therefore we saw four 60 cm long parts off the studs. In order to assemble the frame we connected the corners with long screws and smoothed the edges with sandpaper. We then waxed the frame with natural wood wax to make it waterproof.
After the wax was dry we mounted the door hangers on top of the frame. The GRUNDTAL rails were equally distributed on the frame and assembled onto it with small screws. We used the remaining strip from the GRUNDTAL door hanger for additional hanging opportunities at the bottom of the rack.
Now we can easily hang up our bath towels and still open the door nicely.