Three js Mesh

Edge Position

object.updateMatrixWorld()
const geometry = object.geometry
const positionAttribute = geometry.getAttribute( 'position' )
const vertex = new THREE.Vector3().fromBufferAttribute( positionAttribute, index )
object.localToWorld( vertex )

Box

const geometry = new THREE.BoxGeometry( 1, 1, 1 );
const material = new THREE.MeshBasicMaterial( {color: 0x00ff00} );
const cube = new THREE.Mesh( geometry, material );
scene.add( cube );

show inside

// opacity effect
mesh.material.side = THREE.DoubleSide;
// low effect
mesh.material.side = THREE.BackSide;