Eucharistic Adoration:

Of all devotions, that of adoring Jesus in the Blessed Sacrament is the greatest after the sacraments, the one dearest to God and the one most helpful to us. The Eucharist is a priceless treasure: by not only celebrating it but also by praying before it outside of Mass we are enabled to make contact with the very wellspring of grace."  (Ecclesia de Eucharistica, St John Paul II)