Could you add a few details? Will children be traveling with you (meaning, you'll be looking for activities for young kids?) Is there a budget? Will you have transportation?
The Brown Palace Hotel is certainly a nice place to stay, but it's pretty upscale and expensive.
If you want to remain in downtown Denver, the Denver Mint and the Denver Zoo are fun. If you want to drive, you can drive the Trail Ridge Road near Estes Park, but it's not too close to Denver.
Taking the Pikes Peak cog railway to the top of Pikes Peak is an amazing adventure, but it's in Colorado Springs, an hour south of Denver. The Royal Gorge is amazing, too. You can ride a gondola high above the Gorge for beautiful views for miles and miles. Garden of the Gods in Colorado Springs is a beautiful place to walk and hike.
If you'll be bringing kids, there are several good museums in Denver. Then Denver Capitol building has a plaque embedded in the steps outside where the exact elevation of 5,280 feet is marked. It's fun for kids to know they're a mile high.
If you've never been to Denver, you'll need to be aware of the altitude. Being a mile high can be really difficult to adjust to. You'll need plenty of hydration, and if you go up in elevation (Mt. Evans, Pikes Peak, or any of the other mountains) the temperature can be pretty cold at the top, even if it's warm at the bottom. Don't plan to do too much on the first day if you've never been at a high elevation.
Most ranches will be outside of Denver, near Golden, or Boulder. We have stayed at the Loew's hotel and it was nice.
Also, if you're coming in later fall, some roads close early for the season, or temporarily,because snow falls sooner than expected in the high mountains. Just something to be aware of if you plan to drive through the mountains.
If possible, plan your trip closer to Colorado Springs or Estes Park or Boulder. There are lots more outdoor activities in those areas, if that's the kind of trip you're planning.