The difficulty of doing geotourism in Bulgaria is that most research resources are written in Bulgarian, which I do not speak. Therefore, the science content is going to be a bit thin.
Geology of Building StonesIt’s a frequent tease that to learn about the geology of a region, check out the stones building ancient city walls. In Sofia, this mostly requires getting downstairs to see buildings from when the city was named Serdica. Sofia demonstrates quite a bit of architectural sneakiness, so check courtyards for preserved buildings, inside banks for hidden churches, and within pedestrian overpasses for buried city walls.
The Church of Saint George made my day by containing a few centuries of construction in one shot, with everything from local river stones, cobbles scavenged from nearby Vitosha, and stones imported from far, far away.
As a relic from the communist era, most underpasses are paved in a variety of absolutely beautiful marbles and granites. Although terrifyingly slippery when wet, I did get captured by staring at the stairs often enough the locals probably thought I was insane.
Geology of the Yellow Brick RoadKnyaz (later Tsar) Ferdinand I of Bulgaria entered a marriage of connivance with Princess Marie Louise of Bourbon-Parma on April 20, 1893 in Italy. As a wedding present, the Austro-Hungarian Empire installed yellow paving stones around the palace district (from Largo through Ploshtad Aleksandar Batenburg and down Blvd Tsar Osvoboditel).
I’ve found it difficult to determine a clear source for the yellow bricks. I’m fairly certain they were mined and baked in Buda (possibly from this clay pit), and the bricks themselves only exist in a few cities, including Sofia, Buda, and Vienna.
Mineral Springs & FountainsSofia has several hot springs under and around the city. The springs are accessible by public fountains, and it is not uncommon for residents to collect water from each of the springs for their different mineral compositions.
I was unable to determine exactly how many springs are located in the city, although rumor says around seven or eight, nor what exactly the geothermal situation is under the city. Vitosha, the mountain looming over Sofia, is an 80-million-year-old volcano that’s been folded and uplifted, so is a possible-but-relic heat source. (I didn’t make it up Vitosha, but it seems like a great geo-outing with a “Stone River” of boulders.)
The Museum of Earth & MenThe Museum of Earth & Man has at least 1,242 specimens from 104 countries, representing 30% of the Earth’s mineral species. The informational signs are in Bulgarian, although about three-quarters of the specimens are dual-labelled in Bulgarian & English.
The samples are generally under-lit (particularly the Minerals of Bulgaria), but the collection of rare minerals alone is worth the entry fee. I recommend bringing your own flashlight, and starting your tour by purchasing the only English-language publication for sale in the upstairs back corner: “Earth and Man National Museum Sofia” to use as a guide. The minerals for sale in the gift shop are both more expensive and not as interesting as the typical mall collection.