Cheapest way to make a big trip out of a Rail Pass?

(Well, I already missed the sale, so it can’t be *the* cheapest. But I can do my best.)

If you wanted to make a cross country sightseeing trip in early-mid June, on the smallest budget possible, and only leave the train every three days or so (for hostels and most importantly a shower), what route would you do? Departing from and returning to anywhere on the West coast.

I love national parks and similar nature-based adventures. I’d love to take a detour into Banff and take advantage of the Roam bus line.

I can’t afford long stays in big cities but am happy to stay in a bunk bed and do a cheap walking tour. I’m young and can easily sleep in a coach seat, and can subsist for a long time on prepacked snacks. I’m allergic to shelling out for Ubers but good at navigating public transit.

What journey would you send me on?

Thank you in advance for your ideas!