Either just a thematic piece or an undead-spawning scenario focus
1. Prepare an attractive base
2. Put together a simple box of corrugated cardboard (see picture)
3. Decorate one side of the box to look like an entrance
An effective technique is to cut out shapes of thin cardboard. Once painted they will look like more 3-d then they actually are.
I modelled this way: a door frame, a tympanum and door knobs
4. The columns where modelled using a mixture of PVA glue and plaster
You can get more quality out of green stuff but I can't sculpt so I settled on simple shape with thin parallel lines from top to bottom pressed with a knife.
5. Form the corpulent shape of the mound with a plaster-like putty (filler, spackle or whatever it is called in your country)
Tip: use styrofoam splinters to fill larger volumes. The construction will be more sturdy and you will use less putty.
6. Paint the earth areas green then glue static grass to them
7. Paint the stone/brick areas respectively grey and brick red
You can also use sheets of textured paper from a railway model shop
8. As a finishing touch add some thicker foliage (also available in hobby stores or online as a… "foliage")