The Aldrin Springblossom corvette in X3: Terran Conflict.
Also, it's unlikely the dungeon the sword is in will be uninhabited in fact, the monsters there tend to be very XP-rich anyway. One would think that the time needed to finish the subquest could be better spent on Level Grinding, so the Infinity +1 Sword is often more useful because it has other associated stat bonuses, unique to the character, rather than merely being stronger than other weapons (or so strong that even leveling up can't give you that kind of strength). If you want it, you've got to put the plot on hold and embark on a five-hour sidequest! That, or find the enemy that Randomly Drops it (which will likely be a Metal Slime or Boss in Mook Clothing from the Bonus Dungeon, and the drop rate may be just 2 percent, or 5 percent with a Random Drop Booster). So you'll never get it by just sticking to the game's main story.
This is a weapon, spell, special attack, etc., that is not only the most powerful of its kind in the game (at least for its respective player character(s)), but its power is matched by how hard it is to acquire.
