Return of the Living Dad
So Vile a Sin
Youkali was the home world of the Youkalians. It was later an Earth colony.
Circa 5000 BC, the Osirans and Sutekh battled on Youkali. (Return of the Living Dad)
In 2257, Youkali sent a medical shuttle to Yemaya 4. (Sleepy)
In 2587, Bernice Summerfield and Jason Kane visited Youkali on an archaeological expedition. (Return of the Living Dad)
In 2982, there was a hostage situation on Youkali. (So Vile a Sin)
At some point, The Doctor spent a week cleaning up the after-effects of Daniel Joyce’s visit to Youkali. (Unnatural History)