The Austrian Mint has a beautiful set of niobium and silver bimetallic coins. These are colorful commemorative coins. A second set from Austria is the Architecture Series of coins for Luxembourg.
The Austrian Mint, or Munze Osterreich, is one of the fine mints of the world. One innovative coin series from Austria is the Austrian niobium coin series. I consider the Austrian Mint the leader in niobium and silver coins
The niobium coins are bimetallic, having a 0.900 silver annulus surrounding a niobium inner disk. The inner disk is colorized, but not in using the normal techniques of so many other mints. The inner disk is anodized, which gives it a rich appearance. Other mints colorize with enamel.
One other feature is the coins have related images, one on each side of the coin. Most coins have an image of a person on the obverse, but not these. Instead there are two images unique to the year and consistent with the title of the coin, so the coins are changed on both sides annually.