Here are two photos I took from the Grotto balcony during the April 1, 2006 Spirit of the Liturgy Seminar/Retreat with Fr. Joseph Fessio. For those wondering, what you see in the foreground is the Assumption Grotto Knights of Columbus colorguard.
This was the Saturday Vigil Mass at 4:00pm and, as you can see, the low altar is being used. However, as with all Novus Ordo Masses at Grotto - they are celebrated ad orientem. While the vigil is usually in English, it was celebrated in Latin, with Gregorian chant and sacred polyphony.
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More from Spirit of the Liturgy, with explanations:
Post 2
Post 1