RE Locke and Key:
The original pilot for this series was filmed in 2011 near Pittsburgh in Hartwood Acres County Park, which is built around a spectacular old mansion:
My wife and I hike in the park almost every day, so we saw the whole process, complete with dressing room trailers, catering, blacked out windows for nighttime interior shots, etc, etc. Quite the process
This production apparently had a rocky start with a cancelation and eventual reprieve. I believe none of the footage from this pilot ever made it on the air, but I guess it did its job.
In normal times, you can tour the mansion sometimes. It is especially striking during the holidays. It is a favorite wedding venue--pretty photogenic.
