Iceland has the Althing, one of the world's oldest parliaments.
The Alþingi was founded around 930 at Þingvellir, an assembly site east of modern Reykjavík. During Iceland's medieval Commonwealth, chieftains gathered there to make laws, settle disputes, and hear the elected lawspeaker recite the legal code from the Lögberg, or Law Rock.
The institution's history was not entirely uninterrupted. Iceland came under Norwegian rule in 1262, and the Althing was discontinued in 1800. It was restored in 1845 in Reykjavík and gradually regained legislative importance. Iceland's modern parliament is unicameral and has 63 members.
A common mix-up is treating the Althing as merely a Viking-era gathering. Its origins are medieval, but the present legislature is the modern successor to that assembly. The Isle of Man's Tynwald also makes an ancient-continuity claim, so “oldest parliament” depends on the exact definition used; Iceland is nevertheless the canonical answer to this quiz question.