In Eastern Christianity, Sunday of the Holy Cross, also known as Sunday of the Veneration of the Cross, is celebrated on Third Sunday of Great Lent, and commemorates the Holy Cross and the preparation of the faithful for the commemoration of the Crucifixion during Holy Week. This Sunday falls near the middle of the Great Lent - a period during which Christians are testing themselves by dedicated fasting, abstinence, and prayer - and when a person's strength may be waning as a result. The Holy Cross is remembered and venerated on this day as a symbol that can help restore strength, hope, and grace so that each person can complete the divine struggle of the Fast.
Traditionally, "Apolytikion" and "Kontakion" hymns are recited on this day.
Here are some ways you can observe this day according to Eastern Christian tradition: