Recently Blackthorn Castle was listed as free.  It's similar to the famous Myst.
Your task to to wander around, pick up things, utilize them in other places and solve random puzzles.
There didn't seem to be much of a plot.  And the puzzles themselves weren't too hard.  No need to consult a walkthrough.
Interesting: there are about 65 different scenes.  At any time, you can ask for a clue and it will reveal which scene to go to.  The map on the bottom right lists the location for each scene which is very helpful.  If you pick up a horseshoe, you could wander around and around and try to remember exactly where you might use it. Or you could save all that time with a clue to the location. The game still takes at least 2 or 3 hours to play. The artwork is good. Navigation is a bit awkward in some locations: tap on the bottom center to reverse.

At the very end, I was surprised because solving a certain puzzle and getting the object inside was no different from 20 other puzzles.
https://itunes.apple.com/us/app/blackthorn-castle/id966038711"mt=8

Mystery Lighthouse is very similar. There is a bit more plot. The ending is wonderful.

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