ok,
I'm going to give you an idea to try to open t.
I think it may very well be some sort of makeup case, but it does look to heavy for that.
Really would like to know what it is.
Put on a pair of those rubber coated garden gloves.
Get a small piece of dry ice and have it handy.
I get mine at the grocery store.
With a plumbing torch heat the longer end good and hot
Put the small end on the dry ice and freeze it.
Grab the two ends with the gloves and try to twist them off.
With all the soaking you have done I think this should work.
Good Luck