var multiGallery = {
  init: function() {

    this.overlay = new Element('div', { 'id':'lbOverlay' })
      .addEvent('click', this.close.bind(this))
        .hide().inject(document.body);

    this.gallery = new Element('div', { 'id':'gallery' })
      .inject(document.body);

    this.fx = {
      overlay: this.overlay.effect('opacity', { duration:250 })
    };
  },

  close: function() {
    //...
  }
};

// init gallery when dom is loaded
window.addEvent('domready', function() {
  multiGallery.init();
});