What sort of environment stays interesting month after month after month, though?

I go for a 50 min walk every night with my gf, virtually always the same route, and it's never boring quite the opposite. It's the only time where you have nothing else to do than focus on the essentials, no screen, no music, no food/snacks. Before I met her I did the same alone and it wasn't boring either. If it's boring it probably mean you're addicted to overstimulation

I have a coffee in a park with the wife almost every evening. Park is 2.5 km away from home. If you need a goal, a latte will do.

Ah but you shouldn't drink caffeine past 6pm

You really don't need to tell people not to do the things that they enjoy doing. Most people aren't idiots: they know what works for them.

When I met my wife she would consistently drink a pot of coffee around 8PM and fall asleep an hour later. Different people are wired differently.

Not to disparage your intention here. But couldn't you apply the same argument to this paper's results?

I.e. "Some people don't need to walk 22 minutes a day, don't tell them to do so. Different people are wired differently."

Just as there is evidence walking 22 minutes a day improves lifespan for the /majority/ of people, drinking caffeine 6 hours before bed is considered negative for your sleep for the /majority/ of people. It's sound advice, even if it's telling someone what to do.

While I believe suggesting people be more lenient to other's life choices is good - it's a practice in empathy - sometimes people are misguided because the might not realize the impact of their actions, haven't thought about their actions thoroughly, etc. These mentions can be wakeup calls just as often as they can be negative/annoyances. I'd argue OP keep suggesting advice and instead we all try to keep open minds is the safer choice, for the /majority/ at least.

You can always get decaf or hot chocolate or something else if caffeine bothers you. But of course people have to pick on the use of coffee instead of the advice to have a goal.

Something magical happens to a walk when you do the same route again and again. At some point it stops being routine and turns into something else like you notice things differently each time. With another even more so.

I do a ~25 minute walk basically every day -- the key for me is doing a defined loop. Doesn't matter where, just so long as it's a single loop (eg no repeating, no backtracking) and it always stays interesting for me. And in fact the more you do it, the more it becomes rote, and the LESS you care about the route being interesting. You can just tune out, go on autopilot, and keep thinking about what ever you want to keep thinking about but also get some exercise in.

Just my $0.02

The woods!

The woods are a visual, olfactory, sonic, and proprioceptive environment that is almost overwhelmingly stimulating and ever changing, if you take the time to soak it in.

Facts! That's why I said it as a response to the person asking what walking path could remain interesting month after month!

Around here it's peak mushroom fruiting season. Tons of interesting fungi popping up everywhere! My neighbourhood walks are taking about 10% longer as I stop to take pictures.

Treadmill and a TV?

Walking is a chance to explore your own mind, which should stay interesting.

The woods.

This is a primary reason I live in a real city, of the sort of which are common everywhere but the USA.

Likewise! If you live in a reasonable urban center, walking can just happen in the course of the day, without requiring special time and effort. I never exercise for exercise's sake, but I walk to work, walk to the store, walk to get coffee, walk to the bar, walk to friends' houses; at least 40 minutes of walking every day, often more. It is so much more pleasant than driving everywhere.

Your imagination

Its not about the environment, its about getting out of the damned house and away from distractions. When I go on walks in my neighborhood, thats when the deep thinking happens. Nothing to distract you, just you and your thoughts. I’m not even thinking about where I’m walking to. I’m thinking about all kinds of things. Sometimes the 20 minute walk turns into an hour and I don’t even realize it if I’ve really been pondering.

New York City.

I can't sit still to listen to podcasts, and I soon get bored walking around.

But putting the two together, walking whilst listening to podcasts works very well for me.