Started with a horseback ride. I'd been looking forward to this; unfortunately, this was a group ride. So 20 tourists, packed into thick full-body overalls, plodded along single file on shaggy Icelandic horses. Shrieking German teenagers didn't improve things. I have a lot of riding experience, so I was disappointed, but it might be okay for someone who doesn't ride much. The landscape through which we rode was not terribly interesting, though -- mostly barren lava.
Next, I boarded a bus full of mostly American tourists for the "Golden Circle" tour of the most striking natural wonders near Reykjavík. I despise escorted tours, but I hadn't wanted to go to hassle with renting a car, especially given that I didn't know what the road conditions, the other drivers, and the weather would be like. After going through the tour, though, I think it would be very easy to drive yourself, and next time, I'll rent a car. It was frustrating to adhere to the bus' schedule and priorities.
First stop: Þingvellir National Park. This contains, among other features, the site of the Alþing, the world's oldest parliament, where Icelanders first congregated in 930 AD. We stopped only on a cliff overlooking the valley in which the Alþing's meeting place is located. Driving through the valley after our stop, the bus did not even slow down for us to get a better look at the Alþing site. We likewise trundled right over what our guide quaintly referred to as "The Big Splitting": the chasm where the North American and European tectonic plates are pulling apart. I would think a visible geologic event and the site of the world's oldest representative legislature would be reason to pull over, but evidently the tour company doesn't agree.
We went on to Geysir, site of a group of geysers (geysers were named after Geysir, not the other way around). You wouldn't even slow down for this place if you were in Yellowstone. The Great Geysir is the largest and most famous, but it erupts unpredictably and, at most, once a day. More reliable is Strokkur, which erupts every few minutes. It's pretty cool -- you can see the water start to rise and fall about 30 seconds before an eruption, and a big bubble forms just before the water shoots out.
From there, on to Gullfoss, a massive waterfall that was partially frozen when I saw it. It's absolutely breathtaking and the highlight of the tour.
The final stop of the day was the most irritating: a greenhouse called the Garden of Eden in the little town of Hveragerði. Nothing of interest here: it was a pure tourist trap. It would have been annoying enough to waste time at this pointless visit, but I was even more irked because of the other places we'd seen where I would rather have spent the time.
I highly recommend the Golden Circle tour, but try to do it on your own instead of with a tour.