South Iceland

Sights are listed in west-to-east order:

Þingvellir
this is the most popular national park in Iceland and a UNESCO World Heritage site. It includes a valley that is mentioned in many famous Icelandic sagas and is where one of the oldest parliamentary institutions of the world, the Althing, was founded in the year 930. This is also where tectonic activity can be clearly seen as the continental drift has identified and scarred this area for millions of years. The Þingvellir valley is an older portion of the Mid Atlantic Ridge that is becoming extinct. However, it is still spreading apart at the rate of a quarter-inch per year. This means that the visitor center, perched on the edge of the North American plate with a view of the valley where the Öxará River flows, is moving west, away from the Eurasian plate on the east side of the valley. The valley floor has been dropping by 1.6 inches every century, having dropped a total of 230 feet during the last 100,000 years. Many visitors walk through the smaller Almannagjá rift, that runs along the west edge of the valley, which itself is spreading apart at the faster rate of 0.8 inches per year.
Geysir
the hot spring that is the namesake for all geysers in the world, is also one of the most popular stops in Iceland. First stories of the Geysir area can be found in documents from the year 1294 when earthquakes were frequent in the southern part of Iceland and caused the area to evolve to its current form. In the year 1630 the geysers in the area had so much power that the earth trembled when they spouted. As with many of the natural features in Iceland, many will be amazed at how close you can get to the geysers. Access is very unrestricted, you are not held behind guard rails and no officials warn you off. It is exhilarating to be able to be so close, and refreshing to be treated as an adult. Here's hoping trial lawyers never discover Iceland. As well as Geysir itself, which seldom erupts, there is the five-minutely Strokkur, other geysers, and various strikingly coloured hot pools. There is free parking, a gift shop and a good cafe. Admission 600 ISK.
Gullfoss
Golden Falls - a magnificent 32m high double waterfall on the White River Hvítá. The flow of the river from the regular rains and the glacial runoff, particularly in summer, makes it the largest volume falls in Europe. Numerous tours take you along a Golden Circle that includes Gullfoss. Free parking, gift shop, and cafe.
Kerið
a small volcanic crater on Route 35, about 12 km north of the ring road. Kerið lies conveniently on the route back toward Reykjavik from Gullfoss. There is a small car park, and visitors can walk up to the rim in a matter of seconds, do a circuit of the rim in fifteen minutes, or easily walk down into the bowl on an obvious path. In winter it may be possible to walk out part-way onto the frozen ice of the crater lake. An easy volcano to get up close and personal with! Admission 300 ISK.
Urridafoss waterfall
on the Þjórsá River, Iceland's longest river, has the second-greatest flow of water in Iceland. It is said the salmon in this river have an exceptionally strong and long tailfin in order to clear the 20-foot high waterfall. Directions: turn right off Hwy #1 on a gravel road just before the Þjórsá River, go about 1 km, and turn left on the access road just after passing a farm on the right and crossing a stream.
Seljalandsfoss
one of South Iceland's many falls, falling off a 60 m high cliff. It's biggest attraction is the pathway leading to behind the falls. Access to the falls is free and open year round. Walk about 600 m on the gravel path north from Seljalandsfoss to see the Gljúfrabúi waterfall hidden behind a giant boulder. There are no services at the falls, besides a picnic table and a public bathroom.
Skógar
a small village home to the mighty and beautiful Skógafoss waterfall and one of Iceland's most famous museums, Skogar Folk Museum.Skógafoss is 60 m tall and 25 m wide and comes from the river of Skógá. The falls have been protected since 1987. Access to the falls is open all year round and there is no admission. A trail leads to the top of the falls via metal stairs to the right of the waterfall and up the Skógá river valley. This trail eventually ascends all the way to the Fimmvörðuháls pass between the Eyjafjallajökull and Mýrdalsjökull glaciers before descending to Þórsmörk; the complete hike from Skógar to Þórsmörk generally takes two days. Day hikers can follow this trail as far as they like along the Skógá river, they will be rewarded with views of more than a dozen waterfalls.Skogar Folk Museum houses a large collection of antique and historical artifacts. The museum is stretched over a large area, with 13 houses standing on the museum grounds. The museum is open June to August from 09:00 to 18:30, May and September from 10:00 to 17:00 and the rest of the year from 11:00 to 16:00. Entrance is 1,000 ISK for adults, 600 ISK for students, seniors and children aged 12-15. Free for children under 12 if accompanied by an adult. There are several services in town, including restaurants and accommodation.
Dyrhólaey peninsula
is a nature reserve at the southern-most point of Iceland, with puffins nesting on the cliffs, and a shallow inland lagoon full of wading birds. There are a couple of large sea arches in the cliffs near the point. To the east, you can see the black lava sea stacks of Reynisdrangar. Turn right from the Ring Road onto Rt. 218. Parts of the reserve are off-limits in May and June for bird-nesting, check locally for exact dates and conditions.
Reynisfjara beach
Black volcanic sands become black and grey oval and round rocks as you walk over to the "organ pipe" basalt columns at the Hálsanefshellir sea cave. You can't reach the cave at high tide check tidal times with Icelandic Hydrographic Service, tel. 545-2000, or check Vegagerðin's forecast for the area online. The beach extends 1.5 miles from Reynisfjall to Dýrholaey, providing a barrier that creates the Dyrhólaós Lagoon. Turn right off the Ring Road on Rt. 215 just before you climb the around the last mountain, heading east, before you drop into the small town of Vik.
Vik
this village's beautiful black sand beach provides good views of the Reynisdrangar sea stacks. It is the wettest coastal town in Iceland, getting 7.5 feet of rain annually. There are a half dozen good dining options in Vik including the Hotel Lundi Restaurant, Halldorskaffi, and the Strondin Bistro and Bar.
Skaftárhraun
to the west of Kirkjubæjarklaustur, is one of the world's largest lava plains, covering 4,500 square miles. Despite being covered with moss, it is largely uninhabitable. It was created by an 8-month-long eruption that began in 1783 and produced 3-and-1/3 cubic miles of lava. The eruption and its aftermath dried up several rivers and killed about 25% of the population and 70% of the horses in Iceland. The bad weather it created that probaby helped trigger the French Revolution, and caused the the Mississippi River to freeze in New Orleans and produced ice in the Gulf of Mexico.
Kirkjugólf
literally: Church Floor is an interesting rock formation to the east of Kirkjubæjarklaustur, flat basalt columns that look almost like a man made floor.
itineraries

A Golden Circle tour generally includes – at a minimum – Geysir, Gullfoss, and Þingvellir. Various companies offer day coach tours, or a better alternative is to rent a car for a day; this will let you see many more sights and often save money, especially if you have 2 or more people in your group. This also lets you vary the time you want at each attraction, linger at the geysers, or have a stop at Kerið.