These are fruits of Trichosanthes cucumeroides or Japanese snake gourd at the Institute for Nature Study, i.e., a park or forest in the heart of Central Tokyo. I saw flowers of another gourd Trichosanthes kirilowii or Chinese cucumber in my neighborhood in June this year but that cucumber was entirely got rid of several weeks later, so these Japanese snake gourds half satisfied my curiosity about what Chinese cucumbers look like.
Fruits of the Chinese cucumber and the Japanese snake gourd look like each other except that those of the former are red or orange (like those in these pictures) while those of the latter being yellow.