Tools:
- Polystyrene (general packing stuff nothing fancy)
- Sharp blade (one you dont mind messing up)
- Lighter
- PVA glue
- Flock
- Paints- Grey,black,white,brown
Note* You may need to ventilate the room as part of the process involves cutting through polystyrene with a hot blade, some fumes are produced and are more than likley toxic, it hasn't affected me in anyway although I don't remember having a third nipple :/
You will have to work quick when working with the heated blade!
Heat your blade then quickly make a rough cut out of the hill shape before it cools and gets stuck, if it does just re-heat the blade and continue. This is not a precise practise and generally things you muck up can turn out in your favour ;)

Assume that the blade is heated for each cutting part- Now cut a slope by angling the blade (I've done this for two sides but you can do how many you want)

Next cut some chunks out to form a rock face, again working roughly forms a more realistic look

I also cut some crevices into the top of the hill

- With a cool blade cut some chunks out of where you made a rock face to make some deep crevices

Roughly paint the rocky surfaces Grey

The deep crevices black- I find using a wash/ink or a brush heavy loaded with water best to get right in the nooks n crannies

Paint some brown over where you plan to put the flock down, this is just to stop any white showing through

Add some PVA glue over the brown then add the flock

Touch up the rock surface using a mix of grey and white using a dry brush technique highlighting the more prominent surfaces

Done! (ignore poorly painted minotaur)

And that's basically it, it's not amazing but is good enough for a table and is soooo quick,cheap and easy to do. This is only a small hill but the technique can be applied to larger ones.
Hope this is of use to someone :)
General Awesome