JOEL - I'm not sure about what you mean by "festivals" but I will try to make a list of all the holidays and celebrations we observe.

Pioneer Day - July 24. This annual celebration commemorates the entrance of the first LDS pioneers into the Salt Lake Valley on July 24, 1847. Mormon communities have parades and carnivals and dress up in the clothing of the old pioneers.

Aaronic priesthood commemoration - May 15 - This event is observed to celebrate the restoration of the Aaronic Priesthood which happened on May 15, 1829 when John the Baptist appeared to Joseph Smith. It is usually observed by having a "Fathers and Sons" outing where the fathers and their sons of each local congregation go out on an overnight campout together.

General Conference - twice per year in April and October - All church members meet in Salt Lake City or watch on their TV sets and listen to church leaders give inspirational talks about the gospel of Jesus Christ.

Hill Cummorah pageant - Summer time - Actors perform a reenactment of Book of Mormon stories at Hill Cummorah in Palmyra New York.

Youth Dance Festival - Once per year - Groups of youth of the church perform dances that they have been learning all year. This used to be held every year but recently has been discontinued as an annual event

Mormons observe all the other regular yearly Christian holidays like everyone else, such as Christmas, Easter, Thanksgiving, etc.

Now for the Arts:

Our Temples (different from our local church buildings) usually contain paintings or photographs of Jesus Christ, The First Presidency of the Church, and the 12 Apostles of the Church. Some of the older temples have murals that cover the entire walls of the different rooms. These represent places or events such as the "Garden of Eden", the world, or the creation of the universe. Another room, which represents heaven, is very beautifully decorated with flowers, bright lights, a large chandelier, and beautiful furniture. Smaller rooms, where marriages are performed, have mirrors on opposite walls from each other. When you look into them the repeating reflections seem to go on forever. This represents eternity. There is also a room with a baptismal font that is resting on the backs of twelve oxen, which represent the twelve tribes of Israel.
The architecture of the Temples have important Mormon symbols, such as the beehive; which represents the concept of industry; the sun, moon, and stars, which represent the three degrees of glory in heaven; and the all-seeing eye, which represents the total knowledge, love, and concern that God has for his children. Some temples have a statue on the main spire of a man blowing a trumpet called the Angel Moroni, who was an ancient American prophet talked about in the Book of Mormon.
Our local churches are rather simple but functional on the inside. They usually contain pictures or photographs of Jesus Christ, the Presidency of the church, the twelve Apostles, and the Temple. The outside of the buildings usually have a tall spire either coming out of the ground or out of the top of the building. We do not have crosses on our buildings. To us the cross represents the dying Christ. We like to think about the living Christ instead.