For some time, I have been playing around with the idea of a medieval-like world, but with the twist: Some sci-fi tools exist and are fully operational. But I cannot come up with good and plausible way how this would be possible. 

To make it into points:

* The whole society is pure medieval, before firearms were developed
* But, some people have access to, say, blasters and light sabers (not necessarily both, not necessarily any of it, but basically something completely off the level of that technology level)
* The in-universe explanation would be either "magic" or "gift from Gods", but generally, the people got them, because they found it and guessed the usage by trial and error.

Now I need a plausible, non-magic explanation to make the above possible. And, honestly, I am willing to abandon the whole idea if there is not an explanation at all.

BTW, while typing the question, I might guess your questions, so I have a few more things:

* The high tech weapons (or tools) should be mediocre hard to find. If you need it for your explanation, you may bind them to specific place.
* There may be more than tools. But if you are guessing books or manuals, they can exist and be found, but must be not understandable to current generation (imagine finding nowadays something which comes with a book written in Egypt hieroglyphs)
* Symbolic pictures, or comic books (low level try to communicate something [50 000 years in the future](https://worldbuilding.stackexchange.com/questions/3429/how-might-modern-humans-leave-a-message-for-50-000-years)) may be found, but will come either hugely misinterpreted or not understood at all
* And yes, one idea I have is, that the set up is actually far away in the future and *something happened*. But I am trying to imagine **what exactly happened** and how in the world did it leave so many tech behinf