Thingvellir National Park is an easy drive from Reykjavik, and there are few places in Iceland so important to the Icelandic sense of nationality and character. This is where the Althing - Iceland's general council - first met in 930 and where it continued to meet until 1798.
It's hard to imagine a more fitting site for a parliament. Set at the edge of a great rift valley, where the Mid-Atlantic Ridge tears the earth apart at a rate of some 3cm per year, you must first walk through a deep fissure before reaching the mound where the Althing congregated. Then you emerge and find yourself atop a grassy mound, gazing out over a valley through which runs a sparkling river. Mountains can be seen in the distance, marking the rift boundaries.
In a nod to tourism, a wooden platform has been erected on the mound so you have a sturdy vantage point from which to gaze over the valley and imagine yourself, fur-clad and bone weary after walking the full length of the island, awaiting the very first Althing. After reading the notice boards and soaking up the atmosphere you can take a look at some earthy lumps and bumps - the remains of ancient 'booths' where Althing attendees used to set up temporary home.
You can then follow the path across the river to a second car park, or return to the original if you've no-one to pick you up. The walk is pretty, especially where the river has carved itself a mini canyon through the rock, and gazing at the great rift all around you is a great opportunity to truly absorb the astonishing power of the Earth.
The Althing is well worth a visit, but it's not an all-day attraction. I would heartily recommend making it part of a day trip from Reykjavik, taking in a few other sites as well.