I wouldn't buy bitcoin either, because I would have spend all my time watching the bitcoin price to avoid getting caught out and losing my entire investment. To my mind that is gambling, not investing - not to mention unbelievably stressful.

As far as paying off your house, that might be the best use of your cash. Depends on your mortgage rate, your job, expected job future, and your other potential investment opportunities.

Using myself as an example: I still have two big mortgages, but I have mortgage rates of 0.125% and rather secure 12-month future income streams. Meaning virtually no short term risk there. So I'm looking at tying up some cash in something guaranteeing between 4-7% but the money is bound for 2 years. No, I won't get rich in two years, but I know I won't lose everything. I'll use the next two years paying off my mortgages while developing my skills and trying to increase my income, then reevaluate where things stand in 2 years. Maybe something like that would work for you.