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.
Everything must be carefully plan, although a food business is in demand in the the business but you have to ensure you have the right knowledge in operating such business, it's your passion must be considered as that amount of money we are talking is pretty serious enough.