In no particular order:
1. Rhyolite ghost town, which is more than two hours north of downtown.
2. The defunct Flipperspiel Wunderland pinball joint, back when it was in the same general vicinity as the Pinball Hall of Fame. (It evolved, moved and doesn't really exist these days, but it was an interesting alternative to the famous pinball haven of Vegas.)
3. Mt. Charleston Lodge, a high-altitude restaurant that plenty of people visit, but it's unlikely most Vegas tourists ever venture up the big hill.
4. Valley of Fire, a state park that I find more interesting than Red Rock Canyon, which is closer and therefore draws more Vegas tourists.
5. Freakling Bros. Trilogy of Terror and Las Vegas Haunts (Two local haunted attractions that have been around for years)
6. The Magical Forest, a fundraising holiday light display held during the Christmas season.
7. Wheel of Misfortune (Nobody does a better job of detailing this site better than the fine folks at Vital Vegas: https://vitalvegas.com/wheel-of-misfortune-las-vegas-discovery/)
8. Bonnie and Clyde's death car at Whiskey Pete's Casino in Primm. Plenty of California visitors who drive to Vegas have stopped at these Nevada border casinos, I'm sure. Those of us who fly to Vegas probably don't ever end up in Primm.
9. Searchlight, Nevada: A few years ago we drove to Laughlin late in the afternoon simply because we needed an excuse to drive the BMW convertible I rented more than five miles from our hotel. On the way back we stopped at one of the tiny casinos in Searchlight, which I had stopped at years prior. The casino had Rolling Rock on tap for 50 cents. I splurged and bought a bottle of Bud Light for $1.
10. Colorado River: Last summer I went kayaking below the Hoover Dam. There are plenty of companies offering river excursions, and plenty of people doing them, but those of us who have are likely in the small minority of Vegas tourists who do. I don't sense a lot of people are aware that river kayaking is a thing.
Bonus entries: Grand Canyon Skywalk and Cashman Field (in 2018, the final season the Las Vegas 51s minor league baseball team played its home games there)