I've only ever done this in a custom world that I didn't make, but I'm fairly certain it will work elsewhere
Steps without entering Edit Town:
1. Turn on testingcheatsenabled true
2. Go to the Graveyard (not the Sim!)
3. Shift Click and "Buy On This Lot"
4. Take the eyedropper and go around the lake.
Steps with entering Edit Town:
1. Go the Graveyard
2. Take the eyedropper and go around the lake.
When you see the "Death Fish Spawners" or something or other, click it (do you still have eyedropper on? You better!) If it takes you to a place that has a bunch of white boxes that you've probably never seen before, it worked. If it takes you to the normal Build Community Lot place, try it again after going to live mode. You can add a bunch of "Gem Spawners: Epic." (Again, not exact words!" and within, oh...3 Sim days, there will be Rainbow Gems and Pink Diamonds galore!
I'll edit this up and post a through one soon, but I thought I'd get this out there, since I was pulling my hair out frustrated! (Not really...
)