This NSU cross frame belongs to the collection of the Bad Bruckenau bicycle museum in Germany. It is really something special.
Look at the way the handlebars are constructed, with a brake button in the middle.
Then there's the wonderful meachanism to adjust the chain tension, probably using a left hand and right hand thread.
Really original constructions for this German maker, in years when most German/French/Dutch firms were happy copying the English designs.
By the way: this way of tensioning the chain doesn't work too well, although more producers, like Clément, used the bar to adjust the chain. Problem is: if a rider of some weight (lets say 75 kilo) takes place on the saddle, the whole cross frame starts to 'work' a little. Other firms (like Rudge) used the bar between head and bracket to correct this torsion. In this NSU construction the torsion will only stretch the chain. So when a heavy man uses the bicycle, the chain gets overstretched.
Click the picture to see more pictures of this wonderful bicycle.