~41mm diameter, 23.5 grams; the black background in these pics is actually a proof-like, mirror-finish; it's rim-marked at the bottom "FEINSILBER 1000/000". Stamped on the top rim is "1978", presumably the issue date. I have located the city in Germany; the church is a local landmark and tourist magnet. The date 1499 may be the date the structure was completed, or consecrated. I haven't been able to find any information about why this was issued in 1978, nor how many may have been minted...nothing specific to this medallion. Any illumination of this puzzle will be most welcome, an' thanks for lookin'!
In this case, 1499 is the date of the baptismal font. The church was declared a cultural monument in 1988. Maybe this was part of the campaign leading up to that.
It was in a box filled with foreign coins, mostly silver of a variety of alloys. As the white metal reaches for my threshold of $30, I'm sorting them by fineness for sale as scrap (except for a very few that just may have a bit more value numismatically).