"Our factory was opened fifty years ago."

Translation: Naše továrna byla otevřena před padesáti lety.

[dsarkarati]

What is the difference between "fabrika" and "továrna"?

[hella166755]

Fabrika is only the colloquial espression. In written czech use Továrna.

[endless_sleeper]

Továrna is the neutral word.

Fabrika sounds more expressive, more colloquial. And it's obviously of German origin.

[Willem380762]

What's wrong with 'Před padesáti léty naše továrna byla otevřená'?

[VladaFu]

otevřená - open

otevřena - opened

And byla wants to be in the second position, if not first or final, but that is unlikely here.