People and places in dreams often appear different than they do in waking life, because dreams often use "creative license." What's important to know is that if you feel that something is familiar in your dream even though it looks entirely different, go with the feeling.
You are in your grandparent's house. Houses in dreams are reflections of the self. Here's a link to its definition:
dreamdoctor.com/dream-dictionary/definitions/house.html Grandparents in dreams are often wisdom figures, so on some level you were tapping into that in your dream.
You are eating pizza .Food in dreams is all about nourishment, good and bad. Pizza is often considered a comfort food. Here's a link to its definition:
dreamdoctor.com/dream-dictionary/definitions/food.html
Horizons often represent the future in dreams, as in what's out there ahead of you.
This dream would appear to be about you contemplating what's ahead for you. How did you feel IN the dream, because feelings in dreams are never disguised. How you felt IN the dream is how you feel about its subject in your waking life. Were you curious, happy, concerned, resolved or confused (again, IN the dream)?
More importantly, try to identify what was going on in your waking life at the time of the dream that caused you to have it? It would seem to be all good as you sat there with pizza, in your grandparent's house, thinking about the infinite nature of what was ahead of you.
Your dream is the kind of dream that someone might have as they prepare to graduate from school or college. Please let us know!
Hope that helps!