You missed the first train during the stampede event. Back then there were no adventure stones, you could enter as many times as you wish. I know people farmed a lot, that's why the devs realized they need to implement adventure stones, or they could run out of blockchain items very fast.

With Calamity bow I can clear everything, takes longer to clear the hardest dungeon though, for effective and fast farming the easiest dungeon is the way to go.