The main reason you would want your turtle to spend a little time outdoors is to soak up natural sun. Although you are technically acquiring his UVB needs through UVB bulbs, I strongly believe nature is always better, no matter how sufficient our artificial substitutes can be. Another reason is fresh air, putting him or her closer to the wild than what an enclosed, damp, dust inhabiting, air conditioned space we call our homes can provide. Maybe his or her current aquarium home is a bit on the small side, and letting your turtle into wide space on occasion helps relieve that claustrophobia. Maybe it is to keep things interesting for your turtle by providing him a new world to explore from time to time.
Or maybe you want an outdoor set up just for the fun of it. But keeping your turtle outdoors requires the same amount of time and maintenance as an indoor aquarium, if not more. I have found the cheapest and most practical setup for a turtle is a kiddie pool. I am only regarding solid plastic pools, not inflatable ones. There are certainly other means of creating another setup anywhere from a horse trough to a coy pond, but be practical when making a decision.
The area should be in a great deal of sun; otherwise you are missing the most important aspect of letting your turtle outside. An in ground pond should have excellent filtration and cannot be cleaned with dangerous chemicals, including anti algae if you expect a turtle to stay in there. Horse troughs are excellent for turtles who love deep water, as long as you provide something for him to climb out of to dry off and rest. With that said, there are rules when it comes to sunlight. The number one cause of death by placing your turtle in one of these little pools is heat. I once read a person's question about why her turtle died.
She explained it was perfect 90 degree weather, and a few hours later, her turtle was dead in the water. Although she did not specify, I am certain she did not provide any shade for that animal, or not enough. 90 degree weather might be perfect for a lake or any other large body of water, but a little shallow kiddie pool is not deep enough; it heats up under that summer sun. That is why it is so important to provide shade over the pool. The perfect source for shade is a light obstruction like a plastic table that you can move as the sun moves. Do not place anything on top of the pool like a board; it will just trap heat and make it hotter.
In 90 degree weather, I strongly suggest only providing a little area of sun for your turtle. In 100 degree weather, forget it. In 60 degree, it's just too cold no matter how sunny. Regularly check the temperature of your kiddie pool. I always place a cement block in the pool, because you never know when a gust of wind will come out of nowhere and knock your pool over, dumping your turtle out. I would know, it happened to me.
It was a slightly windy but not terribly gusty day, and after placing my turtle in his pool, I went inside the house. https://shadepundit.com/best-shade-sail-for-patio/ , I stepped back out to find the pool empty and on one side was drenched grass, sand, and my turtle sitting there in a daze. Ever since then, I have always placed something heavy in there. If I hadn't gone back out there until an hour later as I had planned, I would have never seen my turtle again. Even a hawk could swoop down and take an easy meal because the turtle is the only thing in the pool this is another good reason to have a light table to cover some of the pool from an aerial view.
Now the odds of a bird of prey attacking your turtle are so slim, but it's better to be safe and think of all possible threats, according to where you live. So make sure to throw in some fake plants, a cave or two, and a basking area for your turtle. Also, be wary of letting your turtle stay outdoors once it hits late evening. That is when nocturnal animals come out, and if you have raccoons in your area, there is nothing stopping them from snatching up your turtle. Cleaning the pool can be easier than cleaning an aquarium.
Just take out all things in the water sand is the exception and simply lift one side and dump the water out. If you have sand, just be careful not to dump any of it while pouring out the water. When water is depleted, take a hose and wash out any algae, waste, and anything else nasty that will ultimately build up within a day or so. Also, spray down all objects in the pool and wash out the sand thoroughly. Then fill up the water, add dechlorinated formula or let water sit for 24 hours, make sure the temperature is right, and you can throw everything back in.
Without the use of a filter, you will have to do this every day or two. The water should never stink and absolutely no algae. A person could put in a lightweight waterfall filter to the side, and that will delay dumping water out for a week, but I think the former method is more convenient. I said in the beginning the outdoor set up requires the same amount of time and maintenance as an aquarium, yet I make the cleaning process sound easy. That is because of the frequency of cleaning as well as constantly having to check on your turtle due to all the dangers I've mentioned.
It takes a lot of time because once your turtle is placed outdoors, you or someone who knows everything you know has to hourly check on the turtle and the temperature not just look, but feel the water and all that. One hour it's sunny and warm, and in the next, it is storming. As hours go by, you will have to change positions of your shadow in order to keep the water cool. Basically, you cannot throw your turtle in the pool and then go to work. Even a few hours is risking it; one check every hour is the minimum.
Shoot, one time it was only thirty seconds for me, and something went terribly wrong, and only out of luck did it not turn tragic. This is a lot of work, and I suggest no one do this if they don't have the time. As long as your indoor aquarium has adequate space, UVB lighting, and everything else that is required, then an outdoor setup is not necessary. It is just doing something extra for your turtle during the warm seasons.