$100,000 is big amount of money and to double it safety, i think it's impossible, because every doubling method like gambling, trading and investing always have a risk. Maybe investing can be a good one to doubling your money.
Even how good you are in trading you cannot easily double that amount, you need to be lucky at the same time. So in short, it is really hard to find a way to double your amount of money.
Yeah your right it takes a long time before you can make a good profit. but if you choose new altcoin releases you can make a good profit fast but its not easy you can be lose but if you choose legit one like bitcoin and top 20 coinmarketcap you can gain a good profit not fast but for long term.. i am sure you can make a good profit just sell it for the right time.