Daniel,
Looks like a very old Marklin loco to me!
Any marks/numbers on the bottom?
Whatever you do,keep it!
If it is original,and it looks like it,productiondate must be roughly between 1905 and 1915 by Marklin in Germany.
Does it have a windingspring for propulsion?
Does it have a small aircylinder in the roof of the cabin,if yes,this cylinder was to press air to the sound wissle.
Possibly there was a coaltender connected to the loco,do you have that?
Also,i notice the driverods connected to the wheels are missing.
Stop press: i think it is a Marklin 1021 RNN made around 1900 (!),current value around Euro 1,200.- in complete and sound condition.
http://www.antiktoystore.../popup_images/1194_1.JPGThe old Marklin companylogo should show on the smokedoor (front of the engine).
It runs on gauge 1 track.
Cheers,
Paul.