1. Alexander Nevsky Cathedral
This cathedral is absurdly large. Built between 1882 and 1912 to honor the Russian soldiers who died liberating Bulgaria from Ottoman rule, it can hold 5,000 people and its gold dome is visible from almost anywhere in central Sofia. The cathedral sits on its own square, and when you walk up to it, the sheer scale hits you. It is the defining landmark of Sofia, and no list of things to do in Sofia is complete without it. Inside, the atmosphere shifts completely. The nave is dim, lit by candles and thin streams of light through high windows. Frescoes and icons cover the walls, and the air is heavy with incense. The crypt downstairs holds a collection of Orthodox icons spanning several centuries, which is worth the short detour. Photography is generally not allowed inside the main church, though the crypt has its own rules. The square around the cathedral is a must-see in Sofia on its own. On weekends, a small flea market pops up on the south side selling antiques, Soviet-era memorabilia, and old coins. The cathedral is open daily from 7:00 AM to 7:00 PM, and entry to the main church is free.