The Big Ten curves are spectacular, but sorta like Ed said, they're best viewed from a train. As far as Moffat goes, only the west portal is casually accessible, take US40 west to Winter Park. You can get to the east portal via Rollinsville and several miles of unpaved roads. My last two trips through the area found freight traffic to be light-ish, so if you're after maximum action rather than name locations you might factor that into your time budget.
I have an affinity for the
giant HO layout in Greeley. If you're traveling between Cheyenne and Denver in your sightseeing, this is right on your route provided you're following the UP.
Best lodging for trainwatching in Cheyenne is Little America Resort right next to the C&S bridge over the UP. I can't tell you how access is to the Cheyenne facility as the last couple of times I was there were with organized tours, so "on your own" might/might not be tolerated. If you look on maps and notice the US85/87 bridge over the yard and think it might be a great vantage point... forget it. It used to be, but it has since been paneled-off expressly to prohibit use as a viewing perch. It's arguably a "limited access" highway now, it's just disappointing that no consideration was given to the tourist attraction aspects. The UP station has been nicely preserved and contains a museum. BNSF traffic there is moderately light, but UP will be running 'em like streetcars, as usual.
I wish I could fill you in better on lineside railfanning points, but nearly every time through (or to) these locales we've been on a schedule. [sigh]
Don't forget Caboose Hobbies in Denver. Huge LHS. Transcendental experience if you've never been.
