We knows that the crypto currency investment can give us lot of profits even in short time but this is very new there are lot of invesments like real estate,gold,mutual funds silent partner in businesses and lot more but what you think which has highest ROI in short term other than crypto invesments.
My opinion is that real estate can be that one,since my grandfather used to be like buying and selling the lands and made tons of money in his life time but I didn't do that such kind of traditional invetment.
The safest investment of all time is real estate because it increases from time to time due to public demand or accessibility in the area. The land will only decrease once a disaster hit the area like floods or landslides making it not safe to occupy. The only problem in this is you need a large capital, documentation and a lot of tax fees.