Some suggestions:
** As mentioned, the Denver Museum of Science and Nature
** The Denver Zoo
** 16th Street Mall
** Denver Botanical Gardens
** Water World (in Federal Heights)
** The Butterfly Pavilion (in Westminster)
** Catch a show at the Denver Center for the Performing Arts
** Cherry Creek State Park
** Chatfield State Park
** As previously mentioned, Red Rocks (it's not just for concerts)
** As previously mentioned, Coors Brewery (in Golden)
** The Railroad Musuem (also in Golden)
** Tiny Town (near Morrison off US 285)
** Pearl Street Mall (in Boulder)
** Casa Bonita Restaurant (in Lakewood - has cliff divers while you eat!)
** Park Meadows Mall and FlatIrons Crossing Mall are in Highlands Ranch/Centennial and Broomfield, respectively. May be one of those were the malls mentioned to you. Or possibly Cherry Creek Mall in south Denver.
Just some of the things to do besides RMNP.
And speaking of RMNP, if you want to camp INSIDE the park you must make reservations on 01.04.19 for the 4th of July weekend; get up early to do so, as the campgrounds will book very fast. Any date prior to July 4th is likely already booked, including during the week.
There are commercial campgrounds/RV Parks in Estes Park, but again you'll need to book early as these will also fill rapidly.
You'll run into the same problem if you want to camp in Cherry Creek or Chatfield State Parks. Same booking window for those as well.
Trail Ridge Road in RMNP will most likely be open during the time you're visiting. I would encourage you to be there EARLY (as in 8am or before) in order to beat the crowds...and there will be crowds, even during the week. Use the rental car, don't even consider driving your Class C rental on Trail Ridge, as there won't be many places to park it. Old Fall River Road likely won't even be open at all, based on current snowpack reports for our mountains (considerably above average snowpack for this time of year - and snow season is just getting started).
A caveat - there WILL be folks who will try to convince you to bypass Denver and RMNP and go other places. But there's a lot to see and do in Denver, and my suggestions are only the tip of the iceberg.
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