Simple quasi-Celtic key pattern inside an overall Latin Cross shape.  The lighter green horizontal lines at the top and bottom of the cross are connected by a labyrinthine path.
AnonMoos
<p>Self-made image, generated from the following vector PostScript source code:<br clear="all"></p>
<pre>%!
306 484 translate 2.1 dup scale/A 1250 sqrt def/C A 5 add def/B C dup
mul dup add sqrt 50 sqrt sub def/D 1800 sqrt def/E 5000 sqrt def/F
7200 sqrt def/G 28800 sqrt def
0 .1667 0 setrgbcolor C C moveto 0 F rlineto C 2 mul neg 0 rlineto 0 F
neg rlineto F neg 0 rlineto 0 C 2 mul neg rlineto F 0 rlineto 0 G neg
rlineto C 2 mul 0 rlineto 0 G rlineto F 0 rlineto 0 C 2 mul rlineto F
neg 0 rlineto closepath gsave fill grestore 2.5 setlinewidth stroke
7.5 setlinewidth 0 .6667 0.1111 setrgbcolor/linepat{gsave 45 rotate B
neg 0 moveto -10 0 lineto -10 20 lineto 10 20 lineto 10 10 lineto 0 10
lineto 0 -10 lineto -10 -10 lineto -10 -20 lineto 10 -20 lineto 10 0
lineto B 0 lineto stroke grestore }def linepat gsave 0 D translate
linepat grestore gsave D 0 translate linepat grestore gsave 0 D neg
translate linepat grestore gsave D neg 0 translate linepat grestore
gsave 0 F translate linepat grestore gsave F 0 translate linepat
grestore gsave F neg 0 translate linepat grestore gsave 0 F neg
translate linepat grestore gsave 0 16200 sqrt neg translate linepat
grestore gsave 0 G neg translate linepat grestore
A A moveto 0 F rlineto E neg 0 rlineto 0 F neg rlineto F neg 0 rlineto
0 E neg rlineto F 0 rlineto 0 G neg rlineto E 0 rlineto 0 G rlineto F 0
rlineto 0 E rlineto F neg 0 rlineto closepath stroke
2.5 setlinewidth 0 .1667 0 setrgbcolor gsave E neg 0 translate 45
rotate -61.9 15 moveto -48 15 lineto stroke grestore gsave 0 E
translate 45 rotate 48 5 moveto 61.9 5 lineto stroke -41.9 15 moveto
-28 15 lineto stroke grestore gsave 45 rotate 48 -5 moveto 61.9 -5
lineto stroke -48 5 moveto -61.9 5 lineto stroke grestore gsave E 0
translate 45 rotate 48 -15 moveto 61.9 -15 lineto stroke grestore gsave
0 E neg translate 45 rotate -61.9 -5 moveto -48 -5 lineto stroke 28 -15
moveto 41.9 -15 lineto stroke grestore gsave 0 E 2 mul neg translate 45
rotate 18 -25 moveto 31.9 -25 lineto stroke -71.9 -15 moveto -58 -15
lineto stroke grestore showpage
%EOF</pre>
<p>The following is the PostScript source code for the basic square unit of the pattern:
</p>
<pre>%!
300 396 translate 4 dup scale/A 1600 sqrt def/B 35 2 sqrt mul def/C A 5
sub def 0 .167 0 setrgbcolor A A moveto A A neg lineto A neg A neg
lineto A neg A lineto closepath gsave fill grestore 2.5 setlinewidth
stroke gsave 7.5 setlinewidth 0 .76 .2 setrgbcolor C C moveto C C neg
lineto C neg C neg lineto C neg C lineto closepath stroke 45 rotate B
neg 0 moveto -10 0 lineto -10 20 lineto 10 20 lineto 10 10 lineto 0 10
lineto 0 -10 lineto -10 -10 lineto -10 -20 lineto 10 -20 lineto 10 0
lineto B 0 lineto stroke grestore 45 rotate 38 -5 moveto 51.9 -5 lineto
stroke -51.9 5 moveto -38 5 lineto stroke showpage
%EOF</pre>