Here's one that came from Maria, who attended a session I gave recently, and who asks if I can recommend a site where you can "learn ALL the prepositions, if poss. with an example, the pronunciation and a diagram". I'm not sure that I can, Maria, but here's a couple of ideas that I think might work better than such a site, even if you could find one.
In the image, above, a young learner at IH Barcelona has drawn a picture to illustrate "Where's Oscar?", in order to practise and learn the prepositions. In the insets, there are much more complex examples for the same purpose, part of a complete collection of "all the prepositions", produced by design students in their English class (the original idea there came from a dictionary illustration, so long ago that I can no longer remember which dictionary!).
How about a spot of creative writing?
Alternatively, how about getting your learners to see how many prepositions of time and place they can pack into a single story of a limited number of words (say, 120-180, depending on their level).
The start of an example story, for quite a high level:
On a cold starless night in 1858, in a small village outside Astorga, an old man dressed in a threadworn overcoat sat on a bench looking down the road into the trees, expectant…
At a lower, level, you could take the story In a dark, dark wood and get your learners to create their own version (illustrated, with their own artwork, if they're young learners), again incorporating as many prepositions as possible.
If your learners share their stories (think Edmodo, a class blog, a wiki…) and you/they award "prizes" to the best, the most original, the best ghost (etc.) story, and the one with the highest percentage of words that are (correct!) prepositions in the text, and so on, it becomes challenging, creative and fun, as your classroom should be.
How do you learn all the prepositions?
I like these ideas more than a single "site" providing you with practice "exercises". Apart from meeting such words in context — which is going to require extensive reading and listening in order to meet them many times — the learners really have to use them and manipulate them creatively, which they will have to do with these tasks.
Doing the kind of task suggested above collaboratively involves more of that; sharing the end products (after all a huge part of what 21st century technology allows us to do) also means that the learners "meet" the prepositions in context more often, in reading the work their peers produce.
But… if anyone can think of a site like the one Maria was after, do add it to the comments ,-) !