Vatican City, seat of the Roman Catholic church and located entirely withing the city of Rome, Italy issued two Europa Stamps in 2014. The pair feature organs in Vatican churches. These two stamps were a gift from my friend Mark Jameson in Reading, GB. I don't have Scott catalog numbers as my set goes only through 2009.
St John Lateran organ (.70 Euro)
The St John Lateran instrument was begun in the late 1500's and intended to be of the finest and largest in Europe. Biagi built the instrument though the casework was designed and executed by others. Like any prestigious instrument this one went through, or endured, or indeed suffered, from various repairs replacements and enhancements over the years. While some original pipework exists in the instrument, it's very different from the original, though it is now usable by modern musicians in a contemporary worship setting. The most recent extensive work was completed in 1989 with lesser work done in 2002-2003. Four (!) other instruments exist in St John Lateran, an organ for both the Epistle and Gospel transcepts, a very small choir organ and an instrument in Corsini chapel. This wiki gives helpful information, though in Italian.
Choir Chapel Organ, St Peter's (.85 Euro)
The second of the stamp pair shows the Chapel Choir organ in St Peter's Basilica. This is a modern instrument built in 1974 by the Tamburini firm. It's a rather modest instrument of two manuals and pedal. This wiki gives information about all the instruments in St Peter's. A whole book has been written, devoted to the 1875 Cavaille-Coll instrument in the basilica.