Catholics believe the Jesus is uniquely present in the consecrated host. As a result, it is possible to express our love of God when visiting a church where the Eucharist is reserved in a tabernacle.
Here is a short prayer composed by St. Alphonsus Ligouri that focuses on offering to God our love and adoration during such visits to a Catholic church.
My Lord Jesus Christ, who, for the love You bear towards men, remain in this Sacrament night and day, filled with compassion and love, waiting, calling, and welcoming all who come to visit You: I believe that You are present in the Sacrament of the Altar; I adore You from the abyss of my nothingness, and I thank You for all the graces You have given me: particularly for having given me Yourself in this Sacrament, for having given me Your most Holy Mother Mary as my Advocate, and for having called me to visit You in this church.
I pay reverence to Your most loving Heart today, and this for three purposes; first, in thanksgiving for this great Gift; second, to make reparation for all the outrages You have received from all Your enemies in this Sacrament; third, I intend by this visit to adore Youin all the places on earth in which You are present in this Sacrament, and in which You are least honored and most abandoned.
My Jesus, I love You with all my heart.
I repent of having so often displeased Your infinite goodness in the past. I resolve with the help of Your grace not to offend You ever again in the future; and for the present, poor sinner though I be, I consecrate myself wholly to You. I renounce and surrender to You my whole will, my affections, my desires, and all that belongs to me. From this day forward do whatever You please with me and what belongs to me. I ask and desire of You alone Your holy love, final perseverance, and the perfect fulfillment of Your will.