Some people who are so pedant say "you can never end the sentence with a preposition". Some agree, others don't.
There are two types of relative pronouns. One is the type which requires antecedents such as which, who, that, etc. and the other one doesn't always require antecedents. No. 1 is the example for the latter. Some call it headless relative pronoun or relative adverb. Whichever it is called, it has a different function from the former.
I cannot go to the place at (in) which I was raped.
In the above sentence, the antecedent of the relative pronoun which is the place. Without this antecedent, which can't be used. at which or in which can be changed to where as in:
I cannot go to the place where I was raped.
If you put a preposition at or in after "raped", it would be ungrammatical because you are repeating the same preposition twice as in:
*I cannot go to the place at which I was raped at.
The above sentence is marked by * because it is ungrammatical and can't be used. Whenever you find relative adverbs such as when, where, why and how, you don't use a preposition at the end of a sentence.
No. 4 is a construction where the antecedent of where the place is omitted. If you put it back before where, it would be No. 2 sentence.
Note: at in No. 3 sentence is optional as that is broadly used as a relative adverb.
No. 1 and No. 4 sentences have to after go and they are not necessary. You don't need to use to there.