I'm not even scratching the surface here, and many may disagree about any of these being the "top 10", but here are some longer day hikes I did, that are near Denver, and that I thoroughly enjoyed and would do again:

1. Cascade Creek Trail to Crater Lake near Tabernash, CO (starts on the southern side of Lake Granby)

2. East Inlet Trail to Lake Verna (starts on the northern side of Lake Granby)

3. Jasper Lake Trail (near Nederland CO, can take a shuttle from the town to the trailheads)

4. Chicago Lakes Trail by Mt. Evans

Those all fall into a category of hike that you can complete by early-mid afternoon if you start around 7 or 8 AM.

Then there are ton that are 2+ days to complete. The most famous one is the Maroon Bells loop, which I haven't done yet. But one I loved was near Aspen, taking the Maroon Snowmass trail up to Snowmass Lake, camping overnight, and heading back. Most folks extend the trip and summit Snowmass Mountain the next morning.

There are ton of much shorter hikes a very short distance away from Denver that are good to do most of the year. Pretty much anything in Evergreen (Alderfer Three Sisters Trail), Apex Trail near Morrison, Walker Ranch loop by Boulder. Hanging lakes is farther away, but next to Maroon Bells as one of the most famous and highly trafficked hikes.

I've only been here a year and a half and have a lot more to explore.

I've lived in Boulder for six years now, favorite hike is Long's Peak but it's ridiculously long and strenuous. Some good gems that are not as crazy and out of the national park are the Brainard lake area and the Arapahoe glacier trail if you like meadows above treeline.

Just drive West down I-70 into the mountains. There are so many hiking trails just outside the city.

If looking for more of a day trip Pikes Peak is really good too.

If looking for something closer Matthew Winters near Red Rocks is good but normally busy.