Excerpt from an essay on a tour of the ATLAS experiment at CERN.

An entire lifetime thinking, dreaming, breathing physics isn’t sufficient to prepare you; pictures on a screen are flat and shrunken, and that person in frame in the corner is as useful for the scale as would putting a LEGO mini-figure there, and while words on a page can faithfully transmit some of the awe and mystery, they still fit in your hand, trapped on the page.  The final door was unlocked indicating sufficient oxygen concentration, so our guide held it open and ushered us in.  Across the railing was the largest experiment on the largest machine ever created, completely occupying its voluminous cavern save the narrow paths and stairs that hugged the walls, the size of a five-story building but thousands of tonnes heavier, a near-solid mass of billions and billions of pieces of silicon and iron and liquid argon channels and cables and supports and which every piece had descended the shaft from 100 meters above and then was meticulously constructed underground.  The view at this first position was overwhelmed by its entirety and only a part of the end of the experiment, a silicon wheel framed in iron on its cylindrical shape, could be discerned, so we were led single-file to a steep, narrow staircase, gripping the railing and avoiding low-hanging scaffolding, down to the main visitor platform, and looked up.

Despite and precisely because of its size and density, ATLAS was designed to be taken apart perhaps easier than to put together, and we could now see the tracker, usually obscured by 10 meters of metal, slid out of its housing and exposed for maintenance, and framing it on the left was that wheel, 20 marigold wedges of silicon fanned out from the center like rays of the sun, and to the right were those ring electromagnets that produced the toroidal magnetic field, appearing to float around the tracker core, carrying with it the rest of the experiment, ladders, catwalks, and tunnels.  Thousands of cables cascaded from ports on the detached component in front of us, neatly color-coded and orderly strung in streets that merged into boulevards that merged into dense superhighways of lines lashed together with zipties, that, as made of plastic, were immune to the whims and whiles of the magnetic field that drenched the experiment, ensuring that cables always stayed in place.  Craning up our necks, the access shaft continued out of view, a vacuous hole through which everything we could see had to pass, with a dozen pipes along its wall, the largest of which carried all of the air we were breathing at the bottom with fresh air at the top, mixed and circulated by the roaring fans.  It was as if Michelangelo had carted out and was buffing the Pietà in the nave of St. Peters.