Railway Empire 2

Start a custom game on any map and any character selection will do. Importantly, set the year to 1910. Immediately upon starting head to the banking section of the company tab.

Invest your three million dollars in one of the 4 stock market sections, spend every penny of it! For good measure, take out the most expensive bond you can at the same and spend that too (starting later increases the bond size you can take, my guess is inflation!!). You should have just spent between 3.5-4mil on the market.

You can now pause and restart the game to do so again! This method will gain you both investment achievements!