Samhain is a Gaelic festival marking the end of the harvest season and the beginning of winter (the dark half of the year). It is celebrated from sunset on October 31st to sunset on November 1st, which is halfway between the autumn equinox and winter solstice. It marks up the four Gaelic seasonal festivals along with Imbolc, Beltane, and Lughnasadh (Wikipedia, 2013).  
The Celtics believed that at the time of Samhain, that the ghost of the death were able to interact with the living, because the soul of those who died travelled to the otherworld. They lit bonfires in honour of the deaths, and to aid them in their journey and to keep them away of the living. People gathered fruits, vegetables and animals. On this day many creatures were said to be abroad, includIng: fairies, demons, ghost, and all other dark creature (Santino. 2013).

Imbolc or also commonly called Saint Brighid's Day, is a Gaelic festival marking the beginning of spring. It is usually held on the 31st of January to the 1st of February, halfway between the winter solstice and the spring equinox (Danaher, 1994).  Like numerous Celtic festivals, Imbolc centers in the lighting of  fires. In this particular festival, fire was the most important cause it celebrated the  holy day of Brighid, the goddess of fire, fertility and healing. The lighting of fires celebrated the increase power of the sun over the following months. For the christian calendar, this holiday was renamed Candlemas when candles are lit to commemorate the purification of the virgin Mary (Bbc.co.uk, 2006).   

Beltane is the Gaelic May Day festival. It is usually held on April 3oth and March 1st, halfway between the spring equinox and the summer solstice.  Beltane marked the beginning of summer and was when the castle were driving out to the summer pastures. To protect the castle, crops, people, and to encourage growth, rituals were performed. Windows, Doors, and the castle themselves would be decorated with yellow may flowers. Special bonfires were kindled and their flames, smoke and ashes were said to have protective powers. In some parts of Ireland, people would crate may bush; a bush decorated with flowers , ribbons, and bright shells (Wikipedia, 2013)).   

Lughnasadh is a Gaelic festival marking the start of harvest. It is commonly celebrated on July 31st and August 1st, halfway though the summer solstice and the autumn equinox. The festival was named after the god Lugh, it involves great gatherings that included religious ceremonies,  athletic ritual contest, matchmaking, and feasting. Evidence show that the religious ritual consited of offering the first corn, a feast of new food, the sacrifice of a bull and the ritual play dance (wikipedia, 2013).