Originally this hill was much higher, but the top of the hill was removed between 1898 and 1931 to create more flat land for the expansion of downtown Seattle. Based on old photographs of doomed buildings surrounded by steep embankments and sluice machines ( for example, see this photo), it was about 100 feet higher than it's current peak of 165 feet. Sources say that Second Avenue rose 190 feet from Pioneer Square to Lenora Street, but that is likely an underestimate, since Pioneer Square was virtually sea level.
The current high point is in the middle of the intersection of Second Avenue and Virginia Street, next to the Moore Theater. A visitor can tell that all four streets descend from the intersection, but Denny Hill is now left with a paltry prominence of only 35 feet, barely a hill by most standards.