I think lunch, coffee, or just ice cream at Union Station downtown is a great
stealth railfan activity you can do with family, especially if you park at one of the light rail stations and take it into the city center.
From the north-west B-Line in Westminster, passes Rio Grande's North Yard and the BNSF intermodal yard.
From the south (I-25 and Broadway station), goes past the joint line, Burnham Shops, the old Rice Yard area now Elitches and condos.
From the north-east A-Line, passes the UP yard and numerous switchers
If you do this, try and pick a car that does not have those infernal ad-wrap decals, they mar the view.
Best Regards,
Nick