Now to clarify something: I never thought I would try the prostate massage. My sexual experiences have included a variety of unusual things but never something so unusual.
A double penetration dildo or double dildo is a sex toy that allows for the simultaneous penetration of two bodily orifices at the same time.
An 1899 report by Haberlandt documented current and historical use of double-ended dildos in Zanzibar, and is one of the few historical documents of this kind.
While a double dildo obviously would provide stimulation to the wearer as well, the standard straight dildo is very poorly suited for harness use.