1. Go to: http://www.brainfacts.org/3d-brain#intro=false

2. Copy this into console:
THREE.STLExporter = function () {};

THREE.STLExporter.prototype = {

	constructor: THREE.STLExporter,

	parse: ( function () {

		var vector = new THREE.Vector3();
		var normalMatrixWorld = new THREE.Matrix3();

		return function parse( scene, options ) {

			if ( options === undefined ) options = {};

			var binary = options.binary !== undefined ? options.binary : false;

			//

			var objects = [];
			var triangles = 0;

			scene.traverse( function ( object ) {

				if ( object.isMesh ) {

					var geometry = object.geometry;

					if ( geometry.isBufferGeometry ) {

						geometry = new THREE.Geometry().fromBufferGeometry( geometry );

					}

					if ( geometry.isGeometry ) {

						triangles += geometry.faces.length;

						objects.push( {

							geometry: geometry,
							matrixWorld: object.matrixWorld

						} );

					}

				}

			} );

			if ( binary ) {

				var offset = 80; // skip header
				var bufferLength = triangles * 2 + triangles * 3 * 4 * 4 + 80 + 4;
				var arrayBuffer = new ArrayBuffer( bufferLength );
				var output = new DataView( arrayBuffer );
				output.setUint32( offset, triangles, true ); offset += 4;

				for ( var i = 0, il = objects.length; i < il; i ++ ) {

					var object = objects[ i ];

					var vertices = object.geometry.vertices;
					var faces = object.geometry.faces;
					var matrixWorld = object.matrixWorld;

					normalMatrixWorld.getNormalMatrix( matrixWorld );

					for ( var j = 0, jl = faces.length; j < jl; j ++ ) {

						var face = faces[ j ];

						vector.copy( face.normal ).applyMatrix3( normalMatrixWorld ).normalize();

						output.setFloat32( offset, vector.x, true ); offset += 4; // normal
						output.setFloat32( offset, vector.y, true ); offset += 4;
						output.setFloat32( offset, vector.z, true ); offset += 4;

						var indices = [ face.a, face.b, face.c ];

						for ( var k = 0; k < 3; k ++ ) {

							vector.copy( vertices[ indices[ k ] ] ).applyMatrix4( matrixWorld );

							output.setFloat32( offset, vector.x, true ); offset += 4; // vertices
							output.setFloat32( offset, vector.y, true ); offset += 4;
							output.setFloat32( offset, vector.z, true ); offset += 4;

						}

						output.setUint16( offset, 0, true ); offset += 2; // attribute byte count

					}

				}

				return output;

			} else {

				var output = '';

				output += 'solid exported\n';

				for ( var i = 0, il = objects.length; i < il; i ++ ) {

					var object = objects[ i ];

					var vertices = object.geometry.vertices;
					var faces = object.geometry.faces;
					var matrixWorld = object.matrixWorld;

					normalMatrixWorld.getNormalMatrix( matrixWorld );

					for ( var j = 0, jl = faces.length; j < jl; j ++ ) {

						var face = faces[ j ];

						vector.copy( face.normal ).applyMatrix3( normalMatrixWorld ).normalize();

						output += '\tfacet normal ' + vector.x + ' ' + vector.y + ' ' + vector.z + '\n';
						output += '\t\touter loop\n';

						var indices = [ face.a, face.b, face.c ];

						for ( var k = 0; k < 3; k ++ ) {

							vector.copy( vertices[ indices[ k ] ] ).applyMatrix4( matrixWorld );

							output += '\t\t\tvertex ' + vector.x + ' ' + vector.y + ' ' + vector.z + '\n';

						}

						output += '\t\tendloop\n';
						output += '\tendfacet\n';

					}

				}

				output += 'endsolid exported\n';

				return output;

			}

		};

	}() )

};

3. Do this:
var exporter = new THREE.STLExporter();

4. Do this:
var data = exporter.parse( Bapp.Controller.instances["bapp-main-container"].scene.scene, { binary: true } );

5. Do this:
function download(content, fileName, contentType) {
    var a = document.createElement("a");
    var file = new Blob([content], {type: contentType});
    a.href = URL.createObjectURL(file);
    a.download = fileName;
    a.click();
}

6. Do this:
download(data, 'stl.txt', 'text/plain');