1. **Hajj Pilgrimage:** The first ten days of Dhul-Hijjah are considered among the holiest days of the Islamic year. This is the time when the annual Hajj pilgrimage takes place in Mecca, Saudi Arabia. Hajj is one of the Five Pillars of Islam and is obligatory for all Muslims who are physically and financially able to perform it at least once in their lifetime.

2. **Day of Arafah:** The 9th day of Dhul-Hijjah, known as the Day of Arafah, is the pinnacle of the Hajj pilgrimage. Pilgrims gather on the plain of Arafah to pray and seek forgiveness. For Muslims who are not performing Hajj, fasting on this day is highly recommended and is believed to expiate sins of the previous year and the coming year.

3. **Eid al-Adha:** The 10th day of Dhul-Hijjah marks the beginning of Eid al-Adha, also known as the “Festival of Sacrifice.” This is one of the two major Islamic festivals (the other being Eid al-Fitr). It commemorates the willingness of Prophet Ibrahim (Abraham) to sacrifice his son as an act of obedience to God, and in return, God provided a ram to be sacrificed instead. Muslims around the world perform the sacrifice of an animal (usually a sheep, goat, cow, or camel) and distribute the meat to the needy, family, and friends.

4. **First Ten Days:** The first ten days of Dhul-Hijjah are considered especially virtuous. Muslims are encouraged to engage in increased acts of worship, such as prayer, fasting, charity, and reciting the Quran. These days are seen as an opportunity for spiritual growth and earning immense rewards.

Dhul-Hijjah is thus a month of immense spiritual significance, marked by worship, reflection, and community acts of kindness and charity.