Þingvellir, also known as Thingvellir, is a national park in southwestern Iceland, located about 40 kilometers east of the capital city of Reykjavik. It is a site of great geological and historical significance and is regarded as one of Iceland's most important places.

The park is situated in a rift valley created by the separation of the North American and Eurasian tectonic plates, which are slowly moving apart. This has resulted in some unique geological features, including deep fissures, gorges, and volcanic rock formations. Visitors can walk through the Almannagjá gorge, which marks the boundary between the two tectonic plates.

In addition to its geological features, Þingvellir is also an important historical site. It was here that Iceland's first parliament, the Althing, was established in 930 AD, making it one of the oldest democratic institutions in the world. The parliament met here annually, and it was the site of important legal and political decisions. The Althing continued to meet at Þingvellir until 1798, when it was moved to Reykjavik.

Today, visitors can see the remains of the ancient parliament at Þingvellir, including the Lögberg, or Law Rock, where the Lawspeaker would recite the law to the assembled crowds. There are also several churches and other buildings in the area, including a visitor center with exhibits on the park's geology, history, and wildlife.

In 2004, Þingvellir was designated a UNESCO World Heritage Site in recognition of its outstanding geological and cultural significance. It is a popular destination for tourists and locals alike, offering a glimpse into Iceland's unique history and natural beauty.