Describing Feelings is OK
GURPS, like many other systems, has some abilities that involve doing things like sensing emotions. For example, in GURPS 4e the Psychometry advantage reads in part:
You can sense the history of a place or inanimate object - its use, its user's personality, etc. This is usually a supernatural gift of some sort...
On a success, you receive the general sense of emotions and events tied to the object or place... (emphasis added)
I would usually describe the results of using a power like this as "You get a strong feeling of X from the object". For example,
- Scanning a wedding ring = "You feel a strong sense of love and trust coming from the ring."
- Scanning a knife used in a murder = "A powerful aura of fear surrounds the knife. You can see it being raised towards you in a threatening manner."
I would probably describe the magical effects that these places have on people in similar terms.
Constraining Actions is Questionable
It depends on what you're trying to do in your setting, but I would probably stop short of constraining player actions in these places. For example, in a magical garden that gives the people inside a calming sense of peace, I wouldn't make the feeling so overwhelming that it significantly constrains player actions. For example, if a fight somehow broke out inside, the combatants might suffer some kind of penalty, but they would still be able to fight back; I wouldn't say "the feeling of calmness here prevents you from raising your weapon".
If an effect like this is going to meaningfully constrain action, it probably has to apply equally to both players and NPCs. For example, in the Highlander franchise, Immortals were forbidden from fighting on holy ground. This was taken very seriously, to the point that even the most underhanded Immortals didn't risk attacking others on holy ground (the franchise broke this rule a couple of times - in a game, I would make it a clear ground rule and stick to it).