I can understand that at is a location or a point, while in is inside that location. We also use to when we want to express a movement towards a location. I wonder if there is any difference between these pairs of sentences ( Source: Elementary Total English Workbook by Mark Foley and Diane Hall, p. 18 “Correct the mistakes with the verbs. … 3. We swimming at the swimming pool. ___________________ “ 1.We swim at the swimming pool. 2.We go swimming at the swimming pool. The sentences above are correct. I wonder what would happen if I replaced the preposition at with the preposition in. 3.We swim in the swimming pool. 4.We go swimming in the swimming pool. Would there be any significant change in meaning? Could it mean that one wants to stress that the activity takes place inside the pool rather than inside and around it? But one cannot swim around a swimming pool. So the preposition at can only mean inside the pool in this case anyway. Am I right? I think that one could also say: 5.We usually go swimming to the swimming pool and sometimes to the canal. And then the movement toward the location is stressed rather than just the location itself. Am I right? I also wonder if there is any difference between: 6. We are swimming at the swimming pool? 7. We are swimming in the swimming pool? I think that when one is doing the activity one has to use the preposition in rather than the general at. Am I right? In summary: Are sentences 1,2,3,4 basically interchangeable? Is sentence 5 OK? Are sentences 6 and 7 basically interchangeable?