Though we hadn't known it when we booked our Airbnb, we were right around the corner from the Hallgrímskirkja Cathedral tower. In fact, it sat between us and downtown (and dinner).
In simple terms, besides being a focal point for the entire city of Reykjavik, Hallgrímskirkja is a Lutheran Church — services on Sundays, bible studies, book clubs, all the usual Protestant church functions. It's also home to one truly enormous pipe organ.
As we approached the building from the rear, we could hear someone playing that pipe organ — and playing it really well. We continued down the side of the building and around to the front, and found the church doors wide open with people coming and going. After confirming that it was okay to go in, we wandered into the sanctuary and sat to watch this young guy just tearing it up on the organ.
We later found out that we'd stumbled in to a rehearsal by French concert organist David Casson for a performance the next day, part of a summer-long organ concert series. This organ, besides sounding absolutely beautiful, is a beast. It's incredibly complex and requires both hands and both feet to play. Watching David push it, test it, and tweak it, was amazing.
About the organ, the Visit Iceland website says: "Standing tall at an impressive 15m and weighing a remarkable 25 tons, this mechanical action organ is driven by four manuals and a pedal, 102 ranks, 72 stops and 5275 pipes, all designed to reproduce powerful notes capable of filling the huge and holy space with a range of tones - from the dulcet to the dramatic."
Yeah, this was a very cool way to start our Icelandic adventure.