Trading is the best if you can, Don't casinos/gambling...
as OP say he's not going for trading due to its risk and he is really want a risk free investment to multiply his bitcoin,its really hard to find an investment that meet the requirement and more likely will never happen.
OP seems dont like the risk of lossing its bitcoin therefore he would not seek for investments because on such investment it always do involves risk on lossing your money and as we all know that we should risk something to gain something . If you wont risk then you wont gain nothing too, better to keep your bitcoins at all but expect that you would not able to grow your money.