Say you have a corner piece of the dungeon wall, and a bit of rubble on the pointy edge of this corner. Can a Hero move diagonally between the dungeon wall and the rubble piece? I'll try to draw a diagram:

s W W

1 W W

R 2 s

Where:

W - Wall

R - Rubble

s, 1, 2 - free space square

Q1: For instance, in the above 'diagram' (he says using the term loosely), can a hero move from 1 to 2 at the cost of one movement point?

Q2: If he can move (awkwardly), can he fight from square 1 with a monster in square 2?

I suppose there are at least two ways of looking at this. 1, the rubble is piled up in the middle of the square and the hero can move around the edges happily enough, or 2, the rubble has flowed out of the wall and is thus wholey connected to it. I'm sure there are other interpretations. I wanted to disallow the movement but let it fly in the end. The fighting aspect never came up, but it set me wondering.

There is nothing in the rules that prohibit moving or fighting diagonally in that way. I think the 'piled up in the middle' is a good description

We allow it.

The answer to both Q1 and Q2 is YES.

If you look at the JiTD rulebook, the diagrams on page 9 and 10 can be used to answer those questions to a degree. For movement, on page 9 assume the Beastman was the rubble in your example (since both would block movement into that square as you can't move through enemy figures). The diagram shows Silhoutee moving between the two diagnolly so that answers Q1.

For Q2, on page 10 it shows the exact situation you posted and has Silhoutee with LOS to the squares in red shown. If she has LOS, she can attack it in most cases.

I'm sure someone will find fault with this reasoning, but that's always the two examples I've used when explaining the concept to other players.

I find that explaining things with theme are nice, but has no mechanical place in Descent. Rules is rules.