built-in gallery; images are displayed in a grid, full-size images are on separare pages, loading with standard header/sidebar/footer (which can be customized, and re-written to accommodate more space and faster loading time); also missing navigation (back to main page):

envira gallery; all images are in a grid, each full-size image pops up on the same page, with prev/next navigation, and caption below; much faster loading time, users never leave the page; needs size customization: