What is it?

It's time to put on your Sherlock Holmes detective cap for a little investigation. Your mission is to unlock the mystery of this object. Hint: I bought it at the market. (Click on pictures to enlarge.)

It's quite big and somewhat heavy. Let's open it up and see what it looks like inside.

Hm. It's starting to look more and more edible, isn't it? How about if I remove a section and peel off some more of the white skin so we can get a better look?
Amazingly, it now looks very much like grapefruit! However, you can't eat any of the white skin I'm peeling off because it's too rubbery. Moreover, it's juicy and does indeed taste like grapefruit but with none of the bitterness. So... it must be... a shaddock! It's a real treat here in French Guiana because it's refreshing, inexpensive, and big enough to feed a family of six! This shaddock cost me 1€60 and it's one of our favorite fruit here.