@Stacey H.
Here is how I would approach the problem with the goal of narrowing it down to 3-4 top choices with 2-3 hours of research.
(1) Create an Isochronic Map based on how long you are willing to travel. Isochronic maps show you how long it will take to travel to a place based on the mode of transport. You mentioned you don't mind driving or flying to a location, but I'm sure you don't want to have a 10-12 hour travel day to bookend your vacation each time.
Use https://traveltime.com/ to create a map with your desired travel times.
If this were me, I would be willing to travel 2-6 hours in total travel time (Total time = from the minute you leave your house until the minute you walk in the door of your vacation house) So that would restrict me to direct flights out of my nearest airport. So you might want to look up places where you can fly direct from Denver (again an Isocronc map will make this easy)
Now you've completed this step you should have a list of 50-100 cities/towns you have to consider.
(2) Write down "Market Must-Haves" and be ruthless in eliminating markets that don't have those features.
The only features you mentioned were the beach or lake. So come up with a few more absolute market must-haves.
Does population size matter? Do you need to be close to a hospital? Do you care about snow sports? Do you want easy access to other amenities?
Start eliminating markets - again be ruthless
You should be down to 15-20 places now
(3) Determine your "Nice to haves" and then rank your list
Does the market have coffee shops, shopping, other city folks , is it to "hick" or not "hick" enough, do you want to swim in the lake or ocean or just be nearby? Are local hiking trails important and available?
I'm not sure what your preferences are, but create your list, and evaluate each place against your list.
Rank each market and then eliminate everyone but the top 3-5
(4) Do further research into the 3-5 with the goal of eliminating 2-3
This could include searching bigger pockets for that specific market and reading what people are saying. Calling the town's tourism office. Calling a few local hospitality/tourism businesses there to get a feel for the town.
(5) Choose your top 3 and then visit each one
(6) Arrive at your final market choice and then start looking at specific properties with property managers and real estate agents.
(7) Purchase a property and enjoy your new vacation home! (this is the most important step!)