This achievement is for finding and praying at all 50 Health Shrines around the city, every 5 of them increases your health bar by 10% which means at the end you will have double the health you started with.
Fairly early in the game you will meet Amanda and if you go on a date with her it will unlock all the locations on your map for you but the shrines are available from the start so I will post my video guide below for those who wish to get them as early as possible, it splits them into all 4 districts with a decent route to getting them all.