a) Think of a buffet table at a party, or perhaps at a hotel which you've visited.
b) Think of a buffet table at at party, or perhaps at a hotel where you've visited.
Can I use these two sente[n]ces grammatically and, if any, what is difference between two sentences? Please give me some useful tip.
Hello, C.Y.Chang, and welcome to the Grammar Exchange!
Only (a) is correct. The reason you shouldn't say "a hotel where you've visited" is that we speak of visiting something, not of visiting somewhere.
"Visit" is a strongly transitive verb that generally requires a direct object. That is, while we can say, "I visited it", it sounds bad to say, "I visited there."
If you changed the verb to "stayed," you could use "where" after "hotel," because we can say, "I stayed there."
(b1) Think of a buffet table at at party, or perhaps at a hotel where you've stayed.