The St. Peter's Basilica in the Vatican State inside Rome is the largest Christian church in the world. The cathedral covers 23,000 m
2 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.