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.
This would be nice if you have skills for the food business, or if you get guidance from people with experience. In fact, as long as there is the required knowledge, resources and demand, setting up any business could help you to make profit. So, the first step is probably to identify the thing for which you have skills to do, then plan and execute.
Anything you will do should be according to your passion, it would be easy to engage into business where our interest is mainly there. When you have the passion with your business your chances to become successful is higher.