A Plenary Indulgence is granted to the Christian faithful who are devoutly present in a Church or oratory for the singing or recitation of:The indulgence is, of course, subject to the usual conditions. If you are worried by the condition requiring detachment from venial sin, you may like to read my post from last May Plenary Indulgences not impossible.
1. The hymn Veni Creator, either on the first day of the year, imploring divine assistance for the whole of the coming year, or on the solemnity of Pentecost.
2. The hymn Te Deum on the last day of the year, to thank God for the benefits received during the whole of the year that has passed.
In my parish, we'll be singing the Te Deum tonight and the Veni Creator in the morning.