Sunlight Herb

You can't click the door itself, but you might be able to click the ground behind it and walk through.

You CAN click it but it doesn't do anything. I thought I tried several times to walk through them though. I may or may not have tried clicking however. I definitely walked using WASD but the door was solid.

Wow, people actually use WASD? Anyway, I don't know, I know it works for at least one of the blue doors. You might have to get right up to the door, before you can walk through it.

Of course people use WASD, it's the best control method for anything 3rd or first person :)

Or at the very least it's the most familiar. It's in pretty much every single game I can think of...including any other 3D MMO.