The 6th of December is a national holiday in Spain, celebrating the constitution of 1978.
A constitutional referendum was held in Spain on Wednesday, 6 December 1978, to gauge support for either the ratification or repealing of the Spanish Constitution which had been approved by the Cortes Generales on 31 October 1978.
The question asked was “Do you approve of the Constitution Bill?” The referendum resulted in 91.8% of votes in support of the bill on a turnout of 67.1%.
The new constitution replaced the laws of the Franco era, and turned Spain into a constitutional monarchy.
The feat of creating a democratic system without breaking the structures of power of the state was made possible by the approval of the Political Reform act of 1977. The law provided for the legalization of political parties and a democratic election to Constituent Cortes, a committee of which then drafted the Constitution.
Interesting reading:
https://en.wikipedia.org/wiki/Spanish_transition_to_democracy
Interesting viewing: