The Viking invasions, about 700 A.D. brought the greeting of Ves heill to the northernmost coast of Scotland evolving into Waes thu hal, meaning, "be whole" or "good health". The response was drink hail, meaning, "I drink and good luck be to you". By Anglo-Saxon times, the greeting had evolved into people travelling from house to house bringing good wishes and carrying an empty bowl. The master of the house was expected to fill the bowl with hot spicy ale and then it would be passed around to the Wassail (Ves heill) carollers.

The Shetland Islands, and their southerly neighbours the Orkneys, were part of Norway until 1472 when they were ceded to Scotland in lieu of a royal marriage dowry. The most spectacular example of their Viking heritage is displayed each year with the Up-Helly-Aa festival.

Up-Helly-Aa is descended from the ancient festival of Yule, which the Vikings held to celebrate the rebirth of the sun. Yule, or more precisely Jul is a Nordic name for the pagan feast that was celebrated in the middle of January. The Nordic countries still have the ancient word jul and while its origin and actual meaning is unclear the word can be traced back some 2000 years. The word occurs in variations in Germanic languages and as a result it is believed that the jul celebration was a common Germanic feast. (The contemporary festival in Scotland dates from just after the Napoleonic Wars.)

Yule is also known as the Winter Solstice. Activities at midwinter were meant to ensure that the season would renew itself and the days would begin to grow longer again. Greenery was brought into decorate houses - evergreen to symbolize the promise of life to come; mistletoe, believed to hold the life of the host tree even as it appeared to be dead and holly and ivy, symbols of male and female, both necessary for new life.

Up-Helly-Aa is traditionally held the last Tuesday of January. In the morning bearded Vikings (guizers, always men) and their chief Viking, the Guizer Jarl, unveil their elaborate costumes and long boat for spectators. Rather than in private homes as in the past, entertainment halls around town provide suitably extravagant Norse-style hospitality. At night the guizers bearing torches parade through town before burning their full size replica Viking long boat, the revelry continues through to breakfast on Wednesday morning.

If you plan on attending, prepare by reviewing these links
I also suggest visiting The Travel Channel
and typing "Viking Up Helly Aa" in the search engine for a complete listing of events.

Up-Helly-Aa torch procession