We will be celebrating Halloween with an aerial acrobatics show:
But where does Halloween really come from? In short, it comes from harvest celebrations, many cultures around the world had - and some still do - rituals thanking their Gods for the harvest, and this festivals were cleverly substituted by the Roman Empire under the All Saints Day, or All Hallows on the 1st of November, and so the 31st is the eve of All Hallows day or as it was spelled originally - Hallowe’en, where the e'en is short for eve, or evening. The most widely known explanation... 

is that Halloween comes from the Celt festival called Samhain (pronounced sow-in) a name for the end of summer, and therefore the beginning of dark days. This was the end of the harvest and in a way when nature starts to die but also a time day when animals were slaughtered and prepared for winter store, all in all a festival associated with the dead, and the Celts believe that on this day the world of the dead came to the living world.
Similar festivals include the ancient Britons' Calan Gaeaf (pronounced kalan-geyf) - the first day of winter and on the eve the spirits are out so people avoid the places where they gather, like churchyards, stiles, and crossroads.
Feralia and Lemuria are also ancient Roman festivals dedicated to the dead and as in many of these festivals people wore masks and costumes, it's believed that theneed for these guises was to ward off harmful spirits, to confuse the spirits and avoid being possessed, or perhaps to impersonate dead ancestors and spirits whom they wished to communicate with. In the case of Lemuria, dedicated specifically to unburied ancestors who would come back to visit the homes they lived, people had to lure the ghosts out of one's house using specific actions and chants.
The of trick or treating could come from the tradition in many festivals of giving fruit and food to appeased the spirits or from early Christians going around villages collecting soul cakes - bread and with currants - in celebration of the All souls day on Nov. 2nd. The more cakes they collected the more prayers they would give for the souls of the relatives of the donors.

Traditions of "Day of the dead" festivals around the world include the Bon festival celebrated in Japan for more than 500 years and traditionally includes a dance, known as Bon-Odori. The Ayamarka, where the whole of November is devoted to the dead. Touissaint in New Orleans and Dia de los muertos or Day of the dead in Mexico where, like in the Bon-Odori customs involve family reunion and care of ancestors' grave sites. Scholars trace the origins of the Day of the dead to indigenous observances dating back thousands of years.

Other given origin for Halloween is the Roman festival dedicated to Pomona, the goddess of fruits and seeds. Obviously there are hundreds of deities representing fruit, trees, nature and equally many harvest festivals but why single Pomona out, and why would this very festival could be the origin of Halloween? No idea, but there are two curious facts; On the one hand Pomona is a Roman deity with no Greek counterpart and represents both blossoming and harvest. On the other hand Pomona was married to Vertumnus after he "trick" her passing for an old woman (Vertumnus could change his appearance at will, and is also God of of seasons, change and plant growth, as well as gardens and fruit trees) Could it be that the Festival of Pomona also celebrates this "trickery" and can attributed to the disguises? or to the game of apple bobbing?