Located just west of Denver, the Colorado Railroad Museum in Golden is a must see for any railfan. They have operating equipment with specials for every time of year. They have a ton of historic artifacts and items relevant to the history of rail in Colorado. Located in the basement of the main building is the Denver HO Club, who has a large model train layout in the slightly larger HO Scale. Check then out and be sure to plan a visit here

Located up north in Greeley, CO this museum has a variety of artifacts, but ther main attraction is their massive HO Scale layout modeled after the fictional Oregon, California and Eastern railway. They have multiple decks and viewing angles and a fun scavenger hunt. They run trains whenever they are open, with operations often taking place on weekends. Check them out here and make sure you stop if you're a fan of model trains.