Last weekend I....at the....
Last weekend I was/wasn't at the river.
Last weekend I....on the.....
Last weekend I was/wasn't on the island.
Last weekend I....at the....
Last weekend I was/wasn't at the lake.
Last weekend I.....in the .....
Last weekend I was/wasn't in the forest.
Last weekend I....by.....
Last weekend I was/wasn't by the ocean.
Last weekend I....on the mountain.
Last weekend I was/wasn't on the mountain.
Last weekend I....at the....
Last weekend I was/wasn't at the beach.