Morrowind.
I mean, it's a 22 year old game, but since you asked nicely... 🤷♂️
Seeing that silt strider just outside Seyda Neen after the intro to what looked like your run of the mill D&D style fantasy RPG was a surprise, to say the least...
... and it was just the beginning.
It's a real shame later Elder Scrolls games mostly lost that otherworldly feel.