New Mexico:
Of course, Carlsbad Caverns. One of the most amazing sights on the planet, particularly if you love caves. If you have difficulty with the long hike from the natural entrance, you can go down in the Big Room elevator onto paved floor and take the trail around the Big Room, which I assure you is worth the effort. If you can take the full tour, I recommend it. The moment when they turned the lights out (but alas, they don't do that any longer) is the most extreme dark you can get until we get off this planet. There are also special guided tours into new areas of the caverns.
I was amazed how these pictures show up---I used a digital set to 1600 ISO on autofocus and standing very still. The ordinary visual color is the light cream, with, of course, deep shadow, but in the images, a green cast exists with certain lights. Must be some difference in the bulb elements: it makes a very nice contrast. If you want to photograph, I'd advise taking along one of the small hand lights so you can get a little indirect light on some of the more difficult items. My own plan involves a walking-stick camera base, because I'm not as steady as I need to be, particularly on the original trail, where you're constantly descending or climbing.
It's changed enormously since my first visit around 1957. It's self-guided, and that's a bit of a treat, too, the chance to walk at your own pace. It's also accessible by elevator and with paved paths in the Big Room, which contains most of the really grand formations. That walk in itself is very long. We only did half this time. Do not plan to just drop by and buzz through the Big Room: I heartily recommend staying over, getting a good rest and getting an early start. It's 3 hours to do the long walk, and if you're camera bugs like us---allow four. We wore ourselves out and still didn't finish. Which means a return visit. As a side note, if you travel with critters, as we do, take the sun very seriously here. Even on a cool day, cars get hot. We're very careful on this point, and want a good safe place for them to stay while we sightsee.
We stayed at a very nice little motel, the Driftwood, in Carlsbad, which is right down
the road from Lucy's, which is a very excellent Mexican restaurant. The Driftwood doesn't
ordinarily take pets, but it's privately owned, we have a traveling cage, and never leave
the terrible twosome loose in a room unattended. This secured our welcome, and we hope we
were good guests. The rellenos and enchiladas at Lucy's, incidentally, are to die for, and
it's just a couple of blocks down. 
That's our faithful Subaru #2, tail view.
From Carlsbad, we drove right up the main drag to the state highway. In 1957 Last Chance Gas really meant it, and buzzards hovered. Now it's a very fast, good highway.
And it leads, yes, to Roswell, which is a town with a definite sense of humor.
We of course had lunch at the Crashdown Diner. How could we resist? There are more t-shirts to be had in town than you would believe. And a UFO museum, with alien autopsy. I assure you there is also another side to Roswell, which has nice places to stay, etc. But if you collect little green men, or have friends who need a gift, this is a wonderful hour's stop.
From there it was past Kline's Corners (veterans of the old cross-country drive will know that place) and up to Las Vegas---not Nevada: the New Mexican Las Vegas, which has a very nice little motel, pet friendly, and with a restaurant that is hard to get rezzes for. The food is excellent.
For the rest, for anyone east-west bound, I-40 is a splendid drive through amazing territory.
But if you're headed off toward Dallas, try the Raton-Clayton route, which is state highway. If you get onto that one, stop at the Capulin volcano. I recommend reading The Roadside Geology of New Mexico, and getting a good overview of what put all that volcanic debris all over the landscape. This is one of those rare places where you can look close at hand right into the throat of a still standing volcano---an extinct one, to be sure, although one can always be surprised by these things; but the hot spot that created the volcanic field in northern New Mexico should be a dead one, now. It is a special place, and worth the hike around the rim. Bring your walking shoes. The little restaurant at the turn makes good burgers---the 'volcano burger' is a hoot, and very good chili. It's not always open, but is a nice stop when it is.
Capulin Volcano, on the approach. Those are trees up there. It's an easy walk, but it's a long distance around. Since we had the cats in the car on a sunny day, I went back to keep them cool, while Jane took the long walk, and reported an eerie experience on the far rim, where the stunted trees shivered and chattered in the wind. One of these days she's going to kitty-sit and I'll go the whole rim walk.