If you want something simple and free, then puzzles are best suited. I was also looking for a site where they can be collected directly online, without installation or advertising. As a result, I stopped at
Magic Puzzles . It's really convenient there: you open it, select the image you like and calmly assemble it. It's especially nice that new images are added a lot and regularly, so that every time you can choose something to suit your mood. A great option for relaxation.