Taking into consideration the current high volatility, that will probably continue for some time, I think the alts market can be one of the few places where this is possible in a few months... But before investing be aware of the risks, which in fact are high...
Doubling your bitcoin is good but you cannot do it with bitcoin waiting for the time to increase substantially as it will not come easy, you need to wait for longer time before you see it, but there is always an option, invest your bitcoin in ETH, when the price will begin to fall back, the trend is consistent and I am sure you will make money.
Yeah investing in altcoin trading can double your coins over a period of time and its safer in compare to gambling where you depend only on luck to double your coins which unfortunately never happens.