There was a crash when I was trying to the landscaping, during the tour when it said see if you have them and then the next bit I tried it raise, flaten trying different things than it crash and all the tarrains are gone.
If it crashed, and you hadn’t saved, its gone.
You’ll need to start again.
If you had saved and it doesn’t exist anymore, in the project folder there should be an automatic backup of the level from the last time you saved