Lucid dreams are a type of dream where you become aware of the fact that you are dreaming within the dream, then, often, you can direct the dream as you like, go flying, time travel, travel to a distant planet, whatever.

I had a lot of these in my twenties but they declined significantly after that and now in my 60's they are relatively rate even though I still dream quite vividly and generally do remember my dreams at least initially upon wakening.

A key to intentionally having a lucid dream is finding some test to determine if you are awake or dreaming and then doing it frequently while awake. This becomes habit and then you start doing it in your dreams as well.

A test that seems to work for many is looking at their hands though nobody has ever explained to me how this works and what is different in a dream state, however I have not found this to work for me.

I accidentally discovered last night that in a dream state I can not perform simple multiplication in my head. In a dream to solve some problem I had to
multiple 3x17 in my head, I could not do it, but upon waking it was trivial.

I'm not sure how this will work in the long run, if I always use the same numbers
then it will just become a memory item.