This is tough. As much as I love paintings, conceptual art, and sculptures, and wish I could just say, "a HOUSE by Eric Owen Moss", I ultimately think the single-most thing that has ever inspired me is David Hockney's
Pearblossom Highway.

American, California, April 11 - 18, 1986
Chromogenic prints mounted on paper honeycomb panel
78 x 111 in.
97.XM.39
It is ~750 photographs that he took of Pearblossom Highway in California then placed them all together to form the entire scene. AMAZING. He does this a lot, but this piece is my favorite. I am fortunate to have seen it twice in my lifetime. It had already inspired me before I saw it in person. But when I first saw it at the Getty, it was like someone took my heart, and tried to push it out through my eyes. I didn't cry, almost did, but it was that overwhelming as I stood in the same spot with my mouth half-agape for minutes. The second time I saw it at the MOCA, at a David Hockney exhibit. The exhibit had similar stuff that took up entire walls, of the Grand Canyon and other stuff. Tiled pictures he took of human beings, paintings that I'm not all too thrilled about by him, etc. But I turned one corner, saw Pearblossom Highway, and stood in front of it and shook my head in disbelief at how breathtaking it was for a second time.
I'm weird. I love art, but when I visit art museums, I walk through them quickly. It has nothing to do with not appreciating things, it's just how I take things in. If I spend time looking at something longer, it's to see the brush strokes, or how something was done. This is one of a few pieces where I have to stop.
I have a poster of it that I bought from the Getty and it is HUGE, and too big to frame without it costing at least $150 because it'd have to be custom-made. I plan on eventually framing it and putting it on my wall in the house I'm going to settle down in for life, whenever/wherever that's gonna be. It's currently in a cardboard tube in my closet.
One day I'm going to drive down Pearblossom Highway and take a picture of this shot, 22 years later. It will probably be the most meaningful photography escape I'll ever take.