Horn-Bad Meinberg is the location of the Externsteine, a rock formation consisting of several tall, narrow columns. This place was the secret destination of the 3rd Belgian hitchhiking contest. On October 11, 2008, 40 participants hitchhiked from Gent in Belgium towards this spot.
If coming from the west (e.g. Ruhr Area, Paderborn, Kassel) it's best to hitch a ride towards Paderborn. Get out at ramp #26 of the A33, called Paderborn-Elsen. There you'll find a roundabout and the B1, which is leading directly towards Bad Lippspringe and Horn-Bad Meinberg. Try your luck along the street - a good spot might be directly under the bridge - but be aware of bad drivers, it's not really allowed to stand along this way and there's also not much space for stopping cars. Not really recommended after dark.
North-west towards Bielefeld
If you're visiting the Externsteine and want to hitch directly towards Bielefeld or Detmold, just walk from the monuments towards the main road. There you can find a bus stop just on the other side of the road, with a good hard shoulder. Take position there, cars can see you early and it's easy for them to stop. Most might going to Detmold, from there you can hitch your way further towards the A2 and Bielefeld. Don't walk further up the road, it's becomes serpentine and might decrease your chance to get a ride.
South-West towards Paderborn
Just stand at the end of the town at the beginning of Paderborner Straße. This is almost a perfect place.