there is few glitches, that can be used to get to the closed location. Lets call it "bump glitch".

1. Apples or potions or whatever. Just drop it right in front of you. Three or more items will bump u throught the door. its pretty ez, but look at your legs, u must stay at 180 degree angle.

1.1... This feture can be also used by save-load mechanics. Bump yourself, instantly save, then load near the door. Impuls work throught the saves.

2. Telekinesis. Works only with mage (obviosly). Create mana wall into the door. Push yourself into the corner between mana wall and door, u will go thought. Need alot mana and determination.

3. Fireball+hit. Usally i use it with ogre. Not ez, i recomend to save before usage. U need to stay in right degree (180) near the door. Right when ogre hits use fireball.

4. Awfull english. Never write guides, if u dont know difference between present perfect and present perfect continiuos.