Isengar was the younger brother of Hildifons and Belladonna. According to the novels written by J.R.R. Tolkien, Isengar went on an adventure and saw the sea. Going by the timeline, Isengar's age, and the time before Bilbo went on his own adventure, the following scenario illustrates what Isengar and his companions might have done.
After 98 years, the sword Gurthang was reforged by a Gwaith-i-Mîrdain survivor. With the blade completed, the sword was to be returned to the grave of Turin. Thus Gandalf set forth on a quest to help Arda once again.
Adventurers in ca. T.A. 2893 who accompanied Gandalf and Isengar to return Gurthang are as follows: