Unless I use the original version.
If I use the enhanced version then the spacebar doesn't do anything in the first door I meet, which obviously makes the game unplayable.

Suggestions?

Have you tried running the game on BuildGDX?

You can download BuildGDX, and its a much smoother experience, with better mouselook, fully customizable controls, and even gamepad support.

There is also a 4x higher resolution texture pack that you can use with BuildGDX to make the game look much better.

I have that installed for Witchhaven 1 and 2, and its a great experience. You can aslo set a launch path in GOG Galaxy and launch the BuildGDX versions straight from your game page. If you need links to BuildGDX and the texture packs and help getting it installed and running, let me know and I'll help you out.

Here is a link to BuildGDX

https://m210.duke4.net/index.php/downloads/download/8-java/53-buildgdx


Install that in its on folder on your computers drive. Run its, and click on Witchhaven, and in the directory point it to your program files(x86)/GOG Galaxy/Games/Witchaven/Enhanced folder.

Here is a link to the Upscale pack

https://www.moddb.com/games/witchaven/addons/witchaven-upscale-pack-212

Unzip that into the "autoload" folder inside the Witchave/enhanced folder. If you do not have a Witchaven/Enhanced/autoload folder make a folder named autoload inside Enhanced and put the mod files there.

Here is a link to a forum thread explaining how to get the in game cinematics running on BuildGDX. It sound complicated but its really not. All you need is an ISO program like Daemon Tools to mount the ISO's. Then just copy over the SMK files directly into the Enhanced folder.

https://www.gog.com/forum/witchaven/cinematics_on_buildgdx



Let me know if you how this works for you, or if you need any help.

With BuildGDX the Witchaven games are absolutely fantastic and play great.

I don't want to use any other software.
I want to use the game as I bought it and just be able to open the door.

It looks like your problem is that the enhanced version's config remaps the controls to a more "modern" control scheme. It has "E" mapped to open and Space mapped to jump. So try hitting "E" on the door or use the EGSETUP program (in DOSBox) to change the mapping.