Outdoor/Indoor insane asylum
I know of a few haunts that are entirely themed as an insane asylum;
Asylum in Denver
Pennhurst in PA
I think there's one in Vegas but can't remember the name
Terror Behind the Walls in Philly is technically prison themed but you could draw some inspiration from it in some aspects
There's also lots of haunts that have a section themed as an asylum;
13th Floor San Antonio's last few scenes
13th Gate's first "gate" after the elevator ride (VERY well done!)
Knotts had an asylum maze up through last year
Atrox factory has a medical scene (very creative use of old-school railings)
Disturbia has a madical/science lab scene if I remember right
Darkness's infirmary/morgue scene would be great inspiration set-design wise even through it's set in a mortuary not an asylum
Cutting Edge has a few medical scenes which are pretty neat
100 Acres Manor has a hospital portion
SCREAMS south of Dallas has an Asylum haunt
I think of insane asylums as being a blend of hospital and prison, so you could easily incorperate any scene you would find in either of these settings into the haunt in addition to padded rooms and the other strictly asylum themed rooms. Overally, I think it would be a fairly inexpensive theme to do well indoors, but it would cost you a LOT to do the outdoor portions realistically and detailed. My reccomendation would be to have the asylum haunt indoors and then do a haunted trail with a different theme, plus then you get the marketting benefit of 2 haunts in one.
As far as scenes go, there should be plenty that you could choose from. Keep in mind that each could be used more than once if you just switched around the props and layout;
-Receptionsist's desk
-Prison bars
-Medical/surgery room
-Morgue
-Bedrooms
-Freezer
-Electric chair/shock therapy
-Dental surgery
-Padded room
-Staff break room
-Various hallways
-Storage rooms
-Showers/bathrooms
-Etc, etc, etc
Hope this helps!
-Collin
