Golden circle is probably THE touristic route in Iceland, 250km long and doable in a day it takes the visitor to some of the most important sights near Reykjavik, capital of Iceland. Obligatory stops are Þingvellir National Park (also written as Thingvellir), Haukadalur geothermal area and Gullfoss waterfall, other stops might be added, depends on the tour organizer.
We really don't like crowded touristy places, but we also really wanted to see those main sights. So we decided to go anyways, but of course with our rented car and we added a few stops on the route.

Start of the Golden Circle: view of Mt. Esja from the turnoff towards Thingvelir park

Our fist stop was Þórufoss waterfall (also written as Thorufoss), which was supposed to be off the beaten track. Well, not anymore! When we arrived there was a bus full of tourists and their guide was just explaining, that some scenes in Game of Thrones had been shot there. So, you can expect only more and more crowds there.
Anyways, the waterfall is nice, nothing too big or too impressive, but nice. The best part was natural viewing platform, like a small balcony from where you can get really nice photos.

Thorufoss waterfall

Further we drove to Thingvellir National Park, where the continental drift between Eurasian and North American tectonic plates can be seen. In the park you can see the crack very clearly since it is forming a small canyon already! The rock walls are now somewhere between 5 - 10m apart and you can walk between them. Pretty cool! :) Besides the interesting geology of the park it has also significant importance for Icelandic history. In 930 their first parliament was formed at this place and it remained here until 1798, after that it was moved to Reykjavik.

Thingvellir park - too crowded for us!

We mostly wanted to see the crack between the tectonic plates, so we drove to the parking lot. But it was full and the viewing platform was super crowded (and we visited the park in February, which is low season in Iceland!). Our thoughts were: "Should we just drive further? Do we really want to go there?" We didn't feel like walking in the line to see the crack, so we drove further. After about 500m, just after the sign Thingvellir national park, and the bridge over Oxara river, we turned left and found a free and empty parking space. Ideal! And the canyon was right there as well! Lucky us! We enjoyed the walk in the middle of the canyon, trying to remind our selves that we are standing between North America and Europe and that this gap is widening by 2cm annually. The only other living thing that we met was a lovely little white bird rock ptarmigan.

Canyon between the tectonic plates

White ptarmigan has perfect colour for camouflage in the snowy landscape

We wanted to drive further on the road No.550 to another waterfall, but unfortunately it was closed. So we had to follow the touristy route of Golden Circle towards geothermal area of Haukadalur, where the most famous geyser can be found. You can spot this active place from far away, since the steam is coming from almost every rock and the smell of the sulfur is present in the air. This place was one of the highlights of our Iceland trip - we witnessed the geyser eruption - amazingly cool!

Geothermal area ... steam everywhere!

Actually there are two big geysers in the area: Geysir and Strokkur. Geysir was first discovered geyser ever and all the others were named after this one. Until recently it was very active, erupting up to 100m high, but after an earthquake something must have moved underground and it has been quite ever since. Its neighbor, Strokkur however is still very active - erupting every few minutes. It doesn't go as high as Geysir, only about 25m, but it is nevertheless impressive! For us the best part of the whole eruption was a bubble that forms just a second before the actual eruption happens.

Bubble just before the eruption

How does geyser eruption occur? Geyser has a vertical tube connected to the underground reservoirs of water. Important for a geyser to work is that all those reservoirs and tubes are "isolated" with geyserite, special material that is deposited on the walls and is responsible for pressure-tight channels, meaning that the pressure from hot water is carried all the was up to the surface and can't escape through the rocks surrounding the tubes. And this is one of the reasons why we can see the eruption as it is.
Underground water is slowly filling the reservoirs. At the bottom it is heated by heat source (normally hot rocks heated by magma) at the top, however, the fresh underground water is coming cold and it presses down on the hotter water. High pressure from above and high temperature from beneath result is superheated water in the reservoir - this means that water has more than 100°C, but is still liquid. As the reservoir is filling up, the water is getting hotter and hotter. At some point the water at the bottom starts to boil and the bubbles traveling upwards are heating also the water at the top. Eventually the bubbles are so big in size and number that they push the top liquid layer of water out of the vent: as the eruption occurs, first we see a water bubble, which then bursts and the steam goes in the air.

Eruption of a geyser

Strokkur geyser apart, there are also some other geothermal phenomena in this area, like smaller geysers, fumaroles and bubbling mud ... Really incredible place this Haukadalur area. I could watch those eruptions for days, if only the smell of sulfur wasn't so strong.

Smaller geyser

Next stop was Gullfoss waterfall (Golden waterfall in Icelandic) - it is known as one of the most beautiful waterfalls in Iceland. Well, for us it was OK, but nothing special. It actually consists of 2 falls, the upper is 11m high and the lower is 21m meters. For us the letter one was more impressive since this is the place where river Hvita falls into a tectonic crack. You can see very clearly how it used to flow on the same level, where a small canyon has formed already. But then something happened (probably an earthquake), a crack formed and river is now falling into it as a waterfall. Cool, right? :)

The upper waterfall

The lower waterfall, the one that falls in the tectonic crack

Kerið Crater is actually a crater lake now and this was our next stop on the Golden Circle route. We haven't mentioned it yet, but great majority of national parks and other natural attractions are free of charge, so we got a bit spoiled :) And when seeing that we need to pay about 3,5€ for this crater, we decided to skip it, so we drove further. But about 500m later there was a parking lot and we saw a path leading to the top of the crater. So we grabbed the opportunity and started hiking uphill. About 10 minutes later we were at the top of the crater looking down towards the pretty green-bluish lake. The sight was quite amazing and we were even happier that we got to see it for free :) When we came back to the car, there were already 3 other cars parked next to us - I guess we gave the idea to some other budget travelers :)

Kerid crater

How a crater lake is formed: first here was a volcano erupting lava. Later it cooled down, the tubes and dikes remained empty ... after some years the whole empty volcano falls in and a huge hole, a crater is formed. Slowly it is filled with rain, snow, underground water ... and so in the end we can see a crater lake as it is today, with characteristic steep walls and typical conical shape.

Schematic explanation of crater lake formation source: http://www.craterlakeinstitute.com

We concluded our tour with visit to Hellisheiði geothermal power-plant. As already the name says, this power-plant uses natural source (geothermal energy) to produce electricity for the whole city of Reykjavik! But that's not all! It also pumps drinking water and use geothermal energy to heat it up and then send both, cold and hot water to the city, where it is used for heating and for drinking.

Pipes with hot water coming out of the powerplant

In the end our Golden Circle wasn't as touristy as we first feared to be, so we did enjoy it very much, especially the geyser eruption - that was truly the highlight of the day.