I did a google search and found the following information on the Soyal Festival:

Hopi: a solstice purification and renewal celebration of the return of life that begins on the new moon before the shortest day of the year. The major rights which occur approximately eight days before the solstice include a celebration of creation and rebirth dedicated to the Spider Woman and Hawk Maiden. A failed mock attack is made against the holder of the sun shield. This represents the sun's victory over winter's darkness. The Hopi tribe "is dedicated to giving aid and direction to the sun which is ready to 'return' and give strength to budding life." Soyal lasts for 20 days and includes "prayerstick making, purification, rituals and a concluding rabbit hunt, feast and blessing..."

The following excerpt is from the Hopi Cycle of the Year article on the Crossing Worlds site:

"Soyal is the second great ceremony of the and symbolizes the second phase of Creation at the dawn of life. It accepts and confirms the pattern of life development for the coming year. It is often called Soyalangwul, Establishing Life Anew for All the World. This ceremony helps to turn the sun back toward its summer path and implements the life plan for the year. Activities take place in the kiva and include reverent silence, fasting and humility and eating os sacred foods to achieve spiritual focus. Prayer feathers are prepared by the men for every purpose and placed in homes, villages and around the ancestral homeland in shrine sites."

See also the map of the Seasons of the Kachina on the CE Smith Museum of Anthropology site.

Pueblo: There is a six month period, between December and July when kachinas are physically present in the pueblos. The first main ceremony is the Soyal in December which celebrates the return of the sun (winter solstice) and the return of the kachinas to the town from their home in the mountains. The kivas are opened by the Soyal Kachina.

There are also Soyal Kachina dolls.