Thanks for all the ideas! The most sense seems to be reusing it as a building material - to make new concrete (like that!), the slipform walls sound good too!
I've considered rubblekultur and using as a bed by covering with soil and planting high drainage lovers in there. The issue is that it is like 10' from the house and prime space for a shed (existing foundation), and like I mentioned, the rats love it (as do snakes which is great but too close). This is in the city and the rodents are an ongoing issue (we've got lots of cats around, hawks, and the small snakes too).
I'm thinking it makes sense to use this to build a shed / sauna of some sort and maybe retaining walls too. Now I just need to find people who do that kind of work haha.