Fiesta Island can get pretty monotonous, but you can go forever without stopping.

Silver strand on Coronado is the bike leg for a couple of races down here. Nice and flat without many lights.

If you want to go a little north. A cruise up pacific coast hwy from La Jolla all the way up to Oceanside is a fun ride.

as far as pools, I usually swim at 24 hour fitness or open water near fiesta island.

Hope this helps some!

Harbor drive is pretty bad pavement. But it's the best path to get to the bike path that wraps around the south side of the bay and up to Coronado. You can then take the ferry back to downtown or turn around and ride all the way back. Unfortunately downtown isnt the best place to start a ride.

The other bike suggestion I would have is to go out to cabrillo national monument. At the 2nd gate, they'll charge you to enter ($10), but you can just turn around there.

For running, just go to Balboa park or head straight to the bay. The bay has a nice path that's great for running regardless of if you go north or south.