The Botanical Garder Key Hunt in the Tower level that most people are having trouble with and personally took me an hour and a half.
The Blue Key is found on top of the fountain in the starting room, it might be hard to see because it blends in with the sky.
After you've gotten the blue key, fight your way through the plaza to the cafe. Use the blue key on the door and walk up to the balcony (or skip the blue key and cheese your way up to the red key with boxes). The red key will be laying on the ground.
After you get the red key, go down to the gift shop next to the cafe and use the red key. The green key is in this room but it's hard to see with all of the bright colors, its in a glass display case on the counter. after you get this key you can finally open that damned door at the entrance of the plaza.