My group was playing our weekly Pathfinder session and our party was in a T-shaped hallway in a house when the Ranger spotted the big bad at the end of the 'crossbar' portion of the T. They cast Entangle on the square the opponent was occupying. It was decided that the effect spread across the walls (and possibly ceiling) from the point at which it was cast.
Is this how this spell works? After looking it up after the session, it doesn't say it actually creates vegetation and the spell also doesn't state it works on vertical surfaces. So, it appears to be intended for outdoor use only.
Best Answer
Entangle
The spell does not create the vegetation, the vegetation described above needs to exist for the spell to function. If the area is partially covered, only squares that have the required vegetation in them actually count for the purpose of the spell.
It is worth stating that a radius means the spell works in a sphere, focused on the point where you cast it. (often at ground level, so a hemisphere). Any vines and the like that are on walls, or hanging from trees will be affected. The spell doesn't require the plants to be on a flat or horizontal surface.
This lack of creating vegetation is reinforced by the mythic version of entangle (same page) which states
Note that roots are valid for this spell (assume they go out as far as the branches of the tree from the trunk for easy of play), but the trunk and branches of a tree tend not to be (although a weeping willow might count). I personally would recommend allowing anything no thicker than a rope and nothing stiffer than roots to work with the spell (So no young trees) but as usual the final decision is up to your DM.
It is always worth asking your DM / telling your players how exactly your version works when someone takes the spell for the first time.
Try web if/when you get access to it. Web works really well indoors (and is nonfunctional in open spaces).