To double it safely i will build a food business which most people really like. I'll build a restaurant spending all $100k. Although doubling it will require some time but it will be safe in that way. Rather than investing it on some networking or use it as trading capital which have a high risk of doubling money.
I think the build a food business is not easy, it takes time and a good marketing strategy. the fastest way is to join the franchise, joining the business communication I think better than the food.