The St. Peter's Basilica in the Vatican State inside Rome is the largest Christian church in the world. The cathedral covers 23,000 m2
and accommodates 60,000 people.
Used by the Pope for most of the Papal ceremonies like the Easter Vigil Mass.
Right now while I write this on Easter Sunday the large eastern Mass in St. Peter's Square in front of the Basilica take place.
This QTVR by Inaki Rezola is as far as I know the only existing one from inside the Basilica. Photography inside the Basilica is allowed but using a tripod is not allowed which makes it very difficult to do a high Quality Spherical panorama.