From typicallyspanish.com

Fiestas
The December Puente
By m.p.
Dec 5, 2007 - 7:32 AM

The December puente is based around the 6th and 8th of the month. The first of these is the Día de la Constitución Española, or Constitution Day, to commemorate the national referendum which took place on 6th December 1978, when 88% of the people of Spain ratified the new Spanish Constitution which was approved by parliament on 31st October 1978.
The preamble to this historic document states that it is approved with the Spanish Nation’s expressed aims to ‘guarantee democratic coexistence within the Constitution and the laws in accordance with a just economic and social order; consolidate a state of law which ensures the rule of law as the expression of the popular will; protect all Spaniards and all peoples of Spain in the exercise of human rights, their cultures and traditions, languages and institutions; promote the progress of culture and the economy to ensure a dignified quality of life for all; establish an advanced democratic society; and collaborate in the strengthening of peaceful relations and effective cooperation among all the peoples of the Earth.’
It defines Spain as a parliamentary monarchy, and as a social and democratic state subject to the rule of law, and while stating that the Constitution is based on the ‘indissoluble unity’ of the Spanish nation, also assures the right to self-government of the nationalities and regions which form part of the Spanish State: this article of the Constitution essentially established the decentralised political geography of the Spain of today, with 17 regions enjoying a large degree of political autonomy.
The Spanish Constitution came into effect on 29th December 1978, and the day to celebrate the referendum by the Spanish people was established as a national holiday in 1983.

8th December, ‘La Inmaculada Concepción,’ commemorates the Immaculate Conception of the Virgin Mary. Celebrated as a holy day of obligation in the Catholic Church. The date was established as the Feast of the Immaculate Conception in 1476, by Pope Sixtus IV, and was defined as a dogma by Pope Pius IX in 1854.
Mary as the Immaculate Conception was declared as principal patroness of all the possessions of the Spanish Crown in 1760, and has remained the patron virgin of Spain since then.