Wow, it's really confusing. And.. Nora! I thought you are Korean! 간, 가던, and 갔던 can be used before [places]. 제가 간 [서점]은 책이 많았습니다. The bookstore which I visited had many books. 제가 <가던> [제과점]은 빵이 맛있었습니다. The bakery which I <would visit> had nice bread. 제가 갔던 [도서관]은 자료가 많았습니다. The library which I visited had many materials. I can't tell 간 and 갔던 apart. I think we can switch each other. 간/갔던 means "which I went to" or "which I visited" 가던 is somewhat like "would visit" or "used to go to". We don't use that past tense system, 간,가던,갔던 are all past tense. I wrote it only when they are used before places. Nora's answer about "간" is correct!^^

I'm not korean but I'll try my best. They all constit of 가다 (to go) and then different particle is added . So 간 is 가 +는 (example: 내가 간 후에 after I go ) 가던 --> 던 Is used to say ( that I ) so when you want that's the place I go to -- you say 내가 가던 곳이에요 갔던 is exactly like 가던 but in the past tense. I wish this helped you. And make sure to ask a native speaker too. Have a nice day