This is such a gorgeous place to ride in the summer and fall that isn't a far drive and has some idyllic scenery.  It is a perfect beginner trail, especially for those horses who dislike bikes, but is so beautiful that any level rider would enjoy it there.  
Trailers park in the Mud Lake parking lot and there are some nice pull through spots that can handle 4 to 5 trailers.  There are bathrooms in the mud lake parking lot next to the trailer parking that we have always found super clean.  From the Mud Lake parking lot there is a .7 mile trail called the Caribou Ranch link that takes you to Caribou ranch.   There is a 4' wide very non intimidating bridge that runs about 30' long and spans several marshy areas on this trail, so make sure your horses can handle a little bridge work.  Once you get into Caribou Ranch, you will have another bathroom opportunity in the parking lot before hopping onto the Bluebird Loop, which is a 1,8 mile loop on a nice wide and evenly footed trail that goes in and out of the aspens - amazing in the fall!
I have taken barefoot horses here with no problems, on our tender horses, we do boot their fronts as there is one little rocky section to get down on to the loop.  We have only gone here on the weekdays and I have heard the weekends can be super busy, typically we see only a few other hikers on the weekdays.  I am pretty sure we have seen some sort of wildlife every time we have been here, usually deer on the loop, but we have seen Moose and Elk on the drive up a few times.  
The cell service is spotty,  but I know I have had my phone ring a few times here - so there are a few areas of service.  
Overall - A very beginner friendly trail, a long bridge to cross, no water crossings, wildlife, no bikes or dogs.  
Bring with you - Bug Spray, water, snacks, and a camera!
Things to know - Caribou Ranch is closed from April 1st to June 30th for wildlife

https://bouldercounty.gov/open-space/parks-and-trails/caribou-ranch/

This easy to get to trail is great for a quick day ride and I found can be pretty accessible year round.  It is right off of Hwy 66 on the East side of Lyons before hwy 36.
The parking lot has back in spots for 3 trailers, during the week this isn't a problem, but they fill up quick on the weekends.  
This trail is pretty popular and even on the weekdays we frequently encounter lots of other hikers with dogs and bikers.  I like this trail for spicy horses that are new to trail work as it starts off with a longer hill that you can blow your horse out on pretty much from the get go and get them to think a little harder by the time you reach the top.  
I love seeing all the wildlife here, I don't think I have ever gone without seeing at least a deer or two, and during the summer you can pretty much count on seeing snakes (some that rattle). I like to have a shod or booted horse on this trail as it can be pretty rocky in areas.  
There are 3 trails to take here, the Eagle Wind trail, which is the Eastern most trail, makes a nice almost 4 mile loop and is my preferred route.  There are no water crossings on this trail, a great clean bathroom at the trailhead along with a spigot for water, and cell service can be spotty.  
Overall - Beginner friendly - nice quick ride close to town.  
Bring with you - the usual items; water, snacks, jacket, hoofpick and bug spray in the summer.
Things to know - It can get busy on the evenings and weekends, I have heard you can park a trailer down the road past the parking lot, but I have never done this personally.  

​https://bouldercounty.gov/open-space/parks-and-trails/ron-stewart-preserve-rabbit-mountain/

Hermit Park is one of my favorite spots to go to where I can always count on having a great ride that I can make as short or as long as I would like.  
Located just outside of Estes along hwy 36, this area feels secluded, close to the mountains, and has some great areas to pick up a long trot or lope.  I would probably recommend front shoes or boots just as there are some rocky areas, that being said we do have a few equines with super tough feet that I have taken on this trail barefoot many times with no problems.  
The wildlife here is spectacular and I have never gone here without seeing moose, deer, elk, or coyotes.  Parking is super easy with 3-4 nice big spots by the campground, and another place for 2-3 trailers by the Homestead Meadows trailhead at the end of the road.  I have always come here on a weekday and have never seen more than one other trailer and a few other cars... I am sure weekends are probably a different story.   During times of heavy runoff, you can encounter a few little streams here and there, but other than that, water crossings are not something I have seen on this trail.  
They have a great campground for horses with a bathroom close by, each spot has two 12'x12' (ish) pens for horses, a picnic table and a firepit.  Most of the spots are well shaded.  
I typically ride up the Homestead Meadows trail which only stays in Hermit Park for about a mile then connects to some fantastic forest roads that lead to a few older homesteads and some large mountain meadows that are full of wildflowers in the summer.  Wear bug spray though!  I have had the mosquitos be quite hungry in this area.  
Overall - Beginner Friendly but Satisfies the fun for more advanced riders. 
Encounters - Bikes / Hikers / Wildlife  / Dogs on Leashes
Bring - A jacket and raingear (usually at least 20 degrees cooler than the front range), Bug Spray (for you and your horse),  water and snacks (of course), I bring water for my horses, there are a few spigots by the campgrounds, but I wouldn't count on them, and plenty of time to explore - it's easy to spend 4+ hours here!  
Things to know!  No cell service, I occasionally had a few inconsistent spots of service, but nothing to count on.  
Happy Trails!
​(\_/)  Paula