"VERTICAL" DOOR

I honestly think your current setup looks perfectly fine... and I tend to be lamely nit-picky when it comes to visuals! It's pretty clearly implied that there is a doorway there, so the player should be able to figure it out easily enough, I think. =]

If that's not the answer you wanted, sorry!

Make a two-pixel wide grey line with some random darker grey bits for contrast and call it a door.

At that perspective, like that are just A LINE anyway.

If I were to be a huge perspective freak I would tell you to make the bottom bit another pixel wider on each side but it looks find as-is. Maybe you could kill some of the pillow shading by taking off the middle shadow and replacing it with just the lightest shadow? Right now it's a little too smoth to fit in. Like, keep the base color and and shade it with just the shadow used on the top of that table.

you could make a laser instead of a door. Or make events that you can't get pass unless you have the VIP card. I'm not too good with Rm2k, and I'm kinda okay with making stuff, so I could try to make you a laser, you would have to allign it and stuff though.