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.
More from Spirit of the Liturgy, with explanations:
Post 2
Post 1