If you've never had the privilege to see or step inside a one, the experience is quite unexpected. Darker. Seemingly older. Naturally, wood ages differently than stone. The old buildings literally talk as the wood expands and contracts -- snaps. Haunting, yet appealing. And these structures are shared across denominations. Roman Catholic, Greek or Russian Orthodox. Protestant.
One can imagine meticulously surveying extant examples in Finland, Russia, the Czech and Slovak Republics, Hungary, Romania and the Balkans.