Stuff like this has me coming back every so often, last time i ended up just listening to music and driving around.
Eventually i got curious when i saw a sloped wall leading to a flat roof part, i decided to go up there and check the view...turns out it had a dead assassin with a note saying he had to kill a certain person an a roof opposite...so i went there and found another dead npc, but not fitting the name of the assassin's subject with a note saying he had to pick up the subject's coffee and somehow also went on the roof which the subject was known to do.
That little discovery was such a blast.