Please refer to the following Coinquest page ...
Hi Mike --
It's a 20 mark from the old German State of Bavaria (Bayern). The one in my picture sold for $7540 US dollars during an auction last month.
DO NOT CLEAN YOUR COIN. CLEANING RUINS VALUE.
Compare your coin to the one in my photo. The quality of the surfaces appears to be different. Hope not. With different surfaces, yours could be a fake.
Take your coin to a jeweler and have it non-destructively tested (using an XRF analyzer) for gold content. If gold, your coin is genuine. If not, it's a fake.