I knew I was forgetting something. Well, I've omitted lots of wonderful sights, like some of the waterfalls and geological features and glaciers and geothermal fields, but I made no mention at all of Jökulsárlón, where the bus stopped for about 25 minutes. Jökulsárlón is a glacial lagoon, at one tip of the giant glacier Vatnajökull, where chunks of the glacier break off into a tidal lagoon and float around to the delight of visitors before they* head out to sea as icebergs. Little crystal iceberglets wash up on shore for you to eat/crunch/drink if you desire. It's the kind of place where, at least when it comes to the aspect of composition, it's hard to take a bad picture because everywhere you look is stunning. That was definitely one of many "WOWEEEEEEEEEEE" moments on this trip.
(* the glacial chunks, not the visitors)