Religion has retreated into private live. When the settlers left from earth religion had already become a private affair. After the crash and subsequent colonisation of Icarus people banded together against the nex necii and religious or political differences were mostly put aside. The current view on religion is that everybody is free to believe what they want as long as they don't hurt others. 

Remembrance and the Crash Site
The largest religious site on Icarus is the monument of the crash site. People can come to visit to honour the people who lost their lives in the crash. It is a pilgrimage that people who are searching for meaning often undertake. At the site there are priests/acolytes/shamans of the major religious believes who perform rites and also engage in debates and private council. The atmosphere of the site is one of quiet contemplation and acceptance.  
On the site are the last working machines. A computer is carefully preserved (desert dust gets everywhere) as it holds the history of their origins (earth) and the recent history on Icarus. 

Temples and Chapels
Most cities, towns, villages and castles have a small area reserved for prayer and contemplation. This place is open to all who wish to use it and no questions are asked. They also serve as places of refuge.  

Festivals and holidays
Festivals are largely locally organised but some general festivities are observed throughout the planet: 

1. Crash Remembrance Day
Marking the start of their lives on Icarus, Crash Remembrance Day is celebrated each year as a day to be thankful of the past year. This festival occurs on the 10th day of Early Fall.

2. Seasonal & Harvest Festivities
The solstices fall in the middle of each season and are days where a lot of places hold festivities. A common one is the Winter solstice. The weather is cold and the fields are resting. It's also a time with less nex necii activity which allowed the settlers to celebrate even in the earlier years.
Some places have festivities in the Early Spring month to celebrate the planting of crops. Dry regions usually celebrate the spring equinox as it is often a time when the rivers flood and fertilise the land. This festival is also called "Desert Blooming". At the end of Late Summer and the start of Early Fall there are harvest festivals in the more temperate regions.

3. Fairs and Carnivals
Travelling fairs have become more prevalent now that the roads are safer. These travelling performers are diverse. Some host mostly musicians that play for a night of dancing. Others have performers such as jesters, acrobats or actors that perform plays.