Sense Force, also called See Force, or, in the ancient tongue of High Galactic, tactus otium, was a Sense-related Force power. This ability enabled a person to perceive the surrounding Force energy within a specific location. It allowed an individual to discern the strength of the Force present in a given area, individual, or object, and even to determine if that Force was connected to the dark side of the Force, or the light.
To develop and refine this skill, Padawans within the Jedi Order were required to soften their awareness, allowing their surroundings to fade into a generalized haze. Through significant dedication and training, the Force would reveal itself, granting the practitioner insight into the Force signature of a place, unveiling whether it was corrupted, helpful, or harmful.
In certain locations where the dark side of the Force holds considerable influence, this sense could give a Force-sensitive individual a preliminary warning before entering the area. Occasionally, beings could detect the alignment of other Force users, as Yoda did with Dooku. Those proficient in the Force could also attempt to resist this power by hiding themselves, or by being near a nexus of the side they were opposed to.
During his Jedi training on the swamp world of Dagobah, Luke Skywalker employed this Sense-based Force power as he approached the Dark Side Cave on Dagobah. He later made observations about this experience in The Jedi Path: A Manual for Students of the Force.
Guided by the spectral voice of Qui-Gon Jinn's, Master Yoda also encountered the Dark Side Cave, where he experienced a vision of the future Great Jedi Purge along with an illusion of Darth Sidious imploring him to join the dark side.
Qui-Gon Jinn practiced this ability on Coruscant and seemed astonished by the sheer volume of life on the planet.