On an average day at St. Patrick's Cathedral, anywhere from 80 to 100 workers clamber up ladders and across platforms that stretch into the heights of the Neo-Gothic vaulted ceilings. They painstakingly rub masks over marble and plaster surfaces to remove decades of dirt, restore wood detailing to its former luster, and brighten each tiny, luminous shard of the discolored stained-glass windows. It's all part of the ongoing $175 million restoration of the iconic house of worship, which opened its doors in 1879 and last underwent a major fix-up in 1970s. The project started in 2012 and is slated finish up next year. Among the major achievements thus far was to clean the 80-foot spires facing Fifth Avenue, which is why they're no longer shrouded in scaffolding. The ornamented bronze front doors, which weigh 9,200 pounds apiece, were restored at a Long Island City workshop between December 2012 and August 2013. Some pipes from the massive main organ, too, have been removed and shipped off to the Peragallo pipe organ company in Paterson, N.J. for tune-ups, which are now complete. On the practical side, there will be a new fire-safety system. All this, and the church has closed for nary a moment, still hosting a minimum of seven masses a day.