The labyrinth @Mardonis and the solution @prisoner849 gave me the idea of a
BoxBufferLabyrinthGeometry3D.
This should be very easy to generate in many forms.
One result:
I just added it to the collection. Collection of examples from discourse.threejs.org
http://discourse.threejs.hofk.de/
Have fun with it 
<!DOCTYPE html>
<!-- https://discourse.threejs.org/t/how-to-remove-interior-faces-while-keeping-exterior-faces-untouched/4869/19 --> <!-- http://threejs.hofk.de/BoxLabyrinthCreation3D/BoxLabyrinthCreation3D.html -->
<head>
<title> BoxLabyrinthCreation3D </title>
<meta charset="utf-8" />
</head>
<body>
</body>
<script src="../js/three.min.98.js"></script>
<script src="../js/BufferGeometryUtils.js"></script> <!-- not in the core -->
<script src="../js/OrbitControls.js"></script>
<script src="../js/THREEx.WindowResize.js"></script>
<script>
// @author hofk
'use strict';
/*_______________________________________________
icons
The characters on the keyboard have been chosen so that they roughly reflect the form.
wall description
sides l f r b is left front right back, with floor and roof
char sides
G l f r b can only be achieved by beaming
M l f r
C b l f
3 f r b
U l b r
H l r
: f b
F l f
7 f r
L l b
J b r
I l
1 r
- f
. b
without walls
since extra character not possible on the wall
* roof and floor
^ roofless
v floorless
x roofless and floorless
with four side walls but roofless and floorless
#
_________________________________________________*/
var designBoxLabyrinth3D = [
// upper storey first
//23456789.......
[
' M G', // 1
' H ', // 2
' H ', // 3
' F-*--7 ', // 4
' I*7**1 ', // 5
' C:v*L.**:::7 ', // 6
' L*...J U ', // 7
' H ', // 8
' L::::3 ' // 9
],[
' ', // 1
' ', // 2
' ', // 3
' ', // 4
' ', // 5
' # ', // 6
' ', // 7
' ', // 8
' ' // 9
],[
'F::3 ', // 1
'H F:::::7 ', // 2
'H H H ', // 3
'H F-*-7 H ', // 4
'H I****:::1 ', // 5
'L::x***1 H ', // 6
' I...J H ', // 7
' H F:7 L:::7', // 8
' L:::J L:::::J' // 9
]];
var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera( 55, window.innerWidth / window.innerHeight, 0.1, 100 );
camera.position.set( 2, 10, 25 );
var renderer = new THREE.WebGLRenderer( { antialias: true } );
renderer.setSize( window.innerWidth, window.innerHeight );
renderer.setClearColor( 0x111111, 1 );
var container = document.createElement( 'div' );
document.body.appendChild( container );
container.appendChild( renderer.domElement );
THREEx.WindowResize( renderer, camera );
var controls = new THREE.OrbitControls( camera, renderer.domElement );
var texture = new THREE.TextureLoader().load( "brick.jpg" );
var material = new THREE.MeshBasicMaterial( { map: texture , side: THREE.DoubleSide } );
var boxes = [];
var index = [];
var storeys = designBoxLabyrinth3D.length;
for( var f = 0; f < storeys; f ++ ) {
for( var r = 0; r < designBoxLabyrinth3D[ f ].length; r ++ ) {
for( var c = 0; c < designBoxLabyrinth3D[ f ][ r ].length; c ++ ) {
boxes.push( createBox( designBoxLabyrinth3D[ storeys - 1 - f ][ r ][ c ] ) );
}
}
}
var labyrinthGeometry = THREE.BufferGeometryUtils.mergeBufferGeometries( boxes );
var labyrinthMesh = new THREE.Mesh( labyrinthGeometry, material );
scene.add( labyrinthMesh );
animate();
function animate() {
requestAnimationFrame( animate );
renderer.render( scene, camera );
controls.update();
}
function createBox( icon ) {
var g = new THREE.BoxBufferGeometry( );
index = [];
switch ( icon ) {
case 'G': box_G( ); break;
case 'M': box_M( ); break;
case 'C': box_C( ); break;
case '3': box_3( ); break;
case 'U': box_U( ); break;
case 'H': box_H( ); break;
case ':': box_colon( ); break;
case 'F': box_F( ); break;
case '7': box_7( ); break;
case 'L': box_L( ); break;
case 'J': box_J( ); break;
case 'I': box_I( ); break;
case '1': box_1( ); break;
case '-': box_minus( ); break;
case '.': box_dot( ); break;
case '*': box_multi( ); break;
case '^': box_caret( ); break;
case 'v': box_v( ); break;
case 'x': box_x( ); break;
case '#': box_sharp( ); break;
default: box_x( );
}
g.setIndex( index );
// position c, f, r
for ( let xidx = 0; xidx < 72; xidx += 3 ) {
g.getAttribute('position').array[ xidx ] = g.getAttribute('position').array[ xidx ] + c;
}
for ( let yidx = 1; yidx < 72; yidx += 3 ) {
g.getAttribute('position').array[ yidx ] = g.getAttribute('position').array[ yidx ] + f;
}
for ( let zidx = 2; zidx < 72; zidx += 3 ) {
g.getAttribute('position').array[ zidx ] = g.getAttribute('position').array[ zidx ] + r;
}
return g;
}
function px( ) { index.push( 0, 2, 1, 2, 3, 1 ) }
function nx( ) { index.push( 4, 6, 5, 6, 7, 5 ) }
function py( ) { index.push( 8, 10, 9, 10, 11, 9 ) }
function ny( ) { index.push( 12, 14, 13, 14, 15, 13 ) }
function pz( ) { index.push( 16, 18, 17, 18, 19, 17 ) }
function nz( ) { index.push( 20, 22, 21, 22, 23, 21 ) }
function box_G( ) { px( ); nx( ); py( ); ny( ); pz( ); nz( ) }
function box_M( ) { px( ); nx( ); py( ); ny( ); nz( ) }
function box_C( ) { nx( ); py( ); ny( ); pz( ); nz( ) }
function box_3( ) { px( ); py( ); ny( ); pz( ); nz( ) }
function box_U( ) { px( ); nx( ); py( ); ny( ); pz( ) }
function box_H( ) { px( ); nx( ); py( ); ny( ) }
function box_colon( ) { py( ); ny( ); pz( ); nz( ) }
function box_F( ) { nx( ); py( ); ny( ); nz( ) }
function box_7( ) { px( ); py( ); ny( ); nz( ) }
function box_L( ) { nx( ); py( ); ny( ); pz( ) }
function box_J( ) { px( ); py( ); ny( ); pz( ) }
function box_I( ) { nx( ); py( ); ny( ) }
function box_1( ) { px( ); py( ); ny( ) }
function box_minus( ) { py( ); ny( ); nz( ) }
function box_dot( ) { py( ); ny( ); pz( ) }
function box_multi( ) { py( ); ny( ) };
function box_caret( ) { ny( ) }
function box_v( ) { py( ) }
function box_x( ) { }
function box_sharp( ) { px( ); nx( ); pz( ); nz( ) }
</script>
</html>