Hello. I am from Bucharest, Romania - not sure you know where that is, though - I'm just mentioning that so that you can know the climatic conditions from my country-zone. I found this fruit - and a lot more of the same kind - underneath a tree from a park. I'm attaching a photo. I can't effectively describe the smell because I'm not quite sure 'bout it's nature, but I think the photo would be enough for you to figure out. Thanks a lot in advance.
Also known as Osage orange. It is related to the fig and a number of other interesting fruit species in the Moraceae family. The fruit is full of seed which can be extracted and will germinate easily. Or you can put the whole fruit in the ground and a bunch of seedlings will eventually pop up which you can then transplant.
Small, but important point: the English name is correctly Osage-orange, hyphenated to show that it isn't an orange Citrus spp.