Caribbean - 5.5 hours in SJU

I've got a 5 and a half hour layover at SJU and would love to get out of the airport for about 4 hours. Any tips? I assume a taxi to old San Juan, but have not spent anytime on Puerto Rico in about 25 years so not sure what is best?

Any tips? morning to mid afternoon, so maybe a nice long early lunch?

Thanks for your advice.

Also does SJU have any lockers where I could lock up a laptop bag while we go into town?

5 hours... That should be enough for lunch in Old San Juan