In every expansion there is at least one optional trial that you can unlock

Final Fantasy 14 has tons of trials that pit you and seven others against a boss. Most of them are unlocked by doing the game's main scenario quests, but some of them are locked behind side quests.

Those locked behind side quests still have significant rewards, as some of them have "Extreme" versions, where you can earn mounts and other special loot when clearing. Most expansions had an extra trial or two, while three fights were added as part of a longer side quest that greatly expands on the story of characters or areas of the game. In Endwalker, the usual three trials were actually collapsed into the main scenario quests, so there is only one optional trial.

Below we list where you can unlock the normal versions of all optional trials in FFXIV.