The cathedral artifact was an artificial structure created approximately 500 million years prior to the 24th century. It spun on an interdimensional axis with some of its mass spinning into the dimensions of our universe in the Oort cloud of system GQ-12475 in the Gamma Quadrant. Some of its exterior was constructed from gold, platinum, other precious metals, and transuranic elements.
In August 2376 during the Federation Starfleet starship USS Defiant's three month Gamma Quadrant exploration mission, the cathedral artifact was encountered by some of the crew. While on a mission in the shuttlecraft Sagan, Ezri Dax, Julian Bashir, and Nog discovered the structure and became momentarily caught in its interdimensional wake.
Such close proximity to the artifact removed Bashir's genetic enhancements, caused Ezri to reject the Dax symbiont and restored Nog's leg. Thirishar ch'Thane determined, with information provided by Ryek'ekbalabiozan'voslu, that the artifact had shifted the quantum resonance signatures of Bashir, Dax and Nog and was making them incompatible with the universe. (DS9 - Mission Gamma novel: Cathedral)