Pigs in Space
Flying Monkeys
Sent from my iPhone using Tapatalk
There’s a TON of history in Santa Fe. It’s one of the oldest cities in the US, and lots to see just walking around. If you take the train in, stay near or on the central square. The La Fonda is my personal favorite, but there are plenty of choices.
You mentioned “no car” but if you do end up with one, as someone already said, Taos is worth a drive, as is Los Alamos if you have any interest at all in the Manhattan Project. Or even if you don’t - I didn’t, but I stumbled onto a book about it last time I was in Santa Fe, got really interested in the whole thing, and visiting Los Alamos was great fun.
Now you make ME want to go to Santa Fe. It’s been far too long!
Las Vegas is a good base point for a lot of things, some needing travel and some not. Hoover Dam has a lot of bus tours, there are 2-day tours to the South rim of the Grand Canyon, and daylong bus/plane/boat tours of the West part of the Grand Canyon. Red Rock Park and Death Valley probably need a car for a full-day trip (Red Rocks can be done in a half-day), and of course there’s Vegas to see…
Denver has the Mint and a few museums, but the attraction there is the Rockies, which will require a car. Even a better option is Colorado Springs, with the Air Force Academy, several scenic (and wild) caves, Garden of the Gods, and other things that are relatively close (not much driving). A couple days in Denver and a couple more in Colorado Springs are a good option.
Don’t laugh at me, but Prescott, AZ would fit. If you like historic old west stuff, I can give you a monster list of places all within maybe an hours drive. 
It also checks all your other boxes. But you’d need a car…
Fall? Late fall? Go to Reno, then rent a car and take a trip down to Death Valley. November is a popular time to visit there because it is not brutally hot. And if you hit the right spring window in the right year, your could be lucky enough to see stuff blooming.
Bend, Oregon/Crater Lake?
That’s a drive, almost 6 hours. And not as hot in DV, but November for the start of the trip, it can be near freezing.
If you like to eat food, I’ve had some of the best food ever in Las Cruces, New Mexico, and Tucson, Arizona.
Both towns also have mountains near by. You can go and look at the mountains in between mealtimes. Then you can go back into town and have some more food.
How about Flagstaff? You can do day trips to the Grand Canyon, Meteor Crater, Sedona, the Painted Desert, and some cliff dwellings. Maybe some Route 66 stuff too. I haven’t spent lots of time in the city itself but it looks interesting.
Bend Or might be a good candidate if you’re looking for a San Luis Obispo kinda small, kinda quaint, kinda unique kinda place. Probably easier to fly to than Mendacino/Ft Bragg (which I have not been to since the 70’s, so get a different opinion but it’s a pretty long drive from Sacto)
I don’t know it well but Boise certainly doesn’t give me the charm of San Luis Obispo. Someone else might nominate Spokane??? I “hear” its nice but haven’t been there in decades either.
Tucson is, I think, underrated, what with Saguaro NP right there, the big aircraft graveyard at Monahan airbase and a lot of interesting stuff in the greater area. Unlike Phoenix et al, Tucson has actual personality – it may be the personality of a wore-out, retired crack whore, but it is still more than Phoenix has.
Ugh…Phoenix/Scottsdale is the WORST of the bland. Tucson is New Orleans next to Phoenix.
I’ve always liked Mendocino, too, but I’ve not been in over twenty years.
I heartily second Meow Wolf. It was literally trippy for me in that it felt like my mind was expanding when I was there.
Personally, I prefer Taos. It is like Santa Fe for people who are not prepared to deal with Santa Fe. Not a lot going on there, but it has vibe.
If Denver (on your original list) is a possible, might I suggest you look a bit south to Colorado Springs? A smaller downtown, easily walkable, with plenty of pubs/bars/restaurants.
And lots of scenic attractions within easy driving distance (Garden of the Gods, Pike’s Peak).
Relaxing? Cheap? Unique? If you decide to go to the Albuquerque area in the first week of April or October you might consider touring the Trinity Test Site. Open only two days each year you can see where the first atomic bomb was detonated. But you better be a history buff because there’s not much to see or do and getting there is a time consuming chore. I did it back in 2015. It was on my bucket list so I enjoyed the journey. If history is your thing, a trip to Trinity is history is spades. And, if you have extra time during the day, you can also visit the Very Large Array (radiotelescope). It’s another hour’s drive one way but I thought it was worth it too – and it was free that day.
In case you can’t tell, I’m a history and science fan.
Depending on how late spring or early fall, Boise would fit the bill almost perfectly.
There is a hiking/biking/horse riding trail network connecting the foothills to the river with around 200 miles of trails. You could take a multi-day rafting trip on several rivers, book your stay at the Silver City Hotel, go to an event at the historic Egyptian Theater, visit the many old mining towns in the mountains (most are less than an hours drive away) or perhaps go to a wine tasting at one of the many boutique wineries in the area, just to name several off the top of my head.
Boise maybe isn’t the most exciting place to be, but it’s getting there.
Sedona. 90 minutes from the airport in Phoenix, so flight should be easy and cheap. Incomparable scenery. Downtown can get crowded and touristy, but it is really easy to get away from the crowd. More hiking than you could do in a month. Some fantastic resorts in a variety of price ranges. Plus you can recharge your crystals at one of the handy dandy cosmic vortexes.
I spend an enjoyable 4 days in Grand Junction and Glenwood Springs a while back.
Sedona, AZ…hands down
Retired crack whores can be fun to talk to, they have all kinds of stories, plus there’s always the possibility that they may come out of retirement.