Very simple example to start with: a cube diffusing in volume.

The scene.xml file:
<?xml version="1.0"?>
<Scene NB_THREADS="6" DIRECT_PATH="0" VERBOSE="1" NB_PHOTONS="1000"
STORE_TRAJECTORIES="0" STORE_ERROR_TRAJECTORIES="0"
MAX_PATH_LENGTH="1000">
<source NAME="sourceSun0" POWER="1.0" TYPE="sun" SPECTRUM="red">
<dir Z="-1.0" Y="0.3" X="0.2"></dir>
</source>
<spectrum NAME="red" DATA=" 650 1 "> </spectrum>
<camera NAME="cam0" NBPIXELSY="100:" NBPIXELSX="100"
FIELD="30.0" FILTERS="filterR" VOLUME="World" >
<lens Z="3.0" Y="-3.0" X="-3.0"></lens>
<viewPoint Z="0.55" Y="0.5" X="0.5"></viewPoint>
</camera>
<spectrum NAME="filterR" DATA=" 650 1 "> </spectrum>
<surface NAME="cube_surface" MATERIALS="dielectric1" FILE="cube.obj">
</surface>
<dielectric NAME="dielectric1" > </dielectric>
<volume NAME="cube_volume" N="1" MATERIALS="hg2" SURFACES="cube_surface">
</volume>
<Henyey-Greenstein NAME="hg2" LA="10000000" LSTAR="0.1" G="0"></Henyey-Greenstein>
</Scene>
The cube.obj file:
v 0.000000 1.000000 0.000000
v 0.000000 0.000000 1.000000
v 0.000000 1.000000 1.000000
v 0.000000 0.000000 0.000000
v 1.000000 0.000000 1.000000
v 1.000000 1.000000 0.000000
v 1.000000 1.000000 1.000000
v 1.000000 0.000000 0.000000
vn -1.000000 0.000000 0.000000
vn -1.000000 0.000000 0.000000
vn 1.000000 -0.000000 0.000000
vn 1.000000 0.000000 0.000000
vn 0.000000 -1.000000 0.000000
vn 0.000000 -1.000000 0.000000
vn 0.000000 1.000000 0.000000
vn 0.000000 1.000000 0.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 0.000000 1.000000
vn 0.000000 0.000000 1.000000
f 1//1 2//1 3//1
f 4//2 2//2 1//2
f 5//3 6//3 7//3
f 5//4 8//4 6//4
f 8//5 5//5 4//5
f 4//6 5//6 2//6
f 7//7 6//7 1//7
f 7//8 1//8 3//8
f 1//9 6//9 4//9
f 4//10 6//10 8//10
f 7//11 3//11 2//11
f 7//12 2//12 5//12>