Sivarathiri
Sivarathri is the night on which Lord Siva's consort, Umamaheswari was said to have worshipped Lord Siva in accordance with the Vedic tradition. There are 5 kinds of Sivarathiris. These are 1. Niththya Sivarathiri (daily); 2. Patcha Sivarathiri(during the various phases of the moon); 3. Maatha Sivarathiri (Monthly); 4. Yoga Sivarathiri (Spiritual perception) & 5. Maha(the great) Sivarathiri (Annual). Among these 5, Maha Sivarathiri is celebrated with grandeur.

Above: Picture of Lord Siva
In the Indian calendar month of "Maasi" (February/March), during the descending moon at midnight on "Sathurththasi day" (the 14th day of the moon)Lord Siva has been said as have appeared in the symbolic form of a "Lingam". He is therefore refered to as "Lingothpayar". On this occasion, at every 3 hour interval from sunset to sunrise the next morning, special prayers are performed to Lord Siva. This means keeping awake the whole night through. On the following morning, after a bath, one can break their fast.
Some people resort to watching movies to keep awake. This practise defeats the purpose. Instead, it is beneficial to indulge in singing religious songs,hymns or chant the Sri Panchachaara Mantra - "Om Namasivaya" and listen to Siva Puranas (mythological anecdotes relating to Lord Siva). For fasting, drinking milk or water alone is considered satisfactory.
HH Sri Ganapathi Sachchidananda & Maha Sivarathiri
The following video footage took place during a Mahasivarathri celebration. In this video, you will see HH Sri Ganapathi Sachchidananda Swamiji of India, performing a ritual in his own unique and inimitable fashion in a fire pit (Homakunda) & where he usually materialises objects from the fire pit & translates it as a prediction for the year to come.