There are 25 save towers scattered throughout the land. You must save at all 25 to earn this trophy.
You can earn this trophy in your first playthrough but not until you have defeated the first 15 Colossi as one save tower is inaccessible until that point.
Once you have saved at a save tower, it will appear on your in-game map.
This map shows the location of each save tower (as well as each Colossus, shining lizard, and fruit tree). Note that each save tower has a shining lizard associated with it.
Save tower locations:
B-4 Lair on the West
B-4 Lair on the Mesa
B-5 Western Cape
C-1 Umbral Glade
C-3 Western Plain
C-5 Arch Bridge Plain
D-2 Stone Arch Gorge
D-5 Blasted Lands
D-7 Southwestern Cape
E-1 Dried Marsh
E-3 Ravine Entrance
E-3 Round Stone Hill
E-4 Stone Bridge Cliff
E-5 Autumn Forest
F-2 Northern Span
F-4 Shrine of Worship
F-7 Southern Plain
F-8 The Broken Seal (inaccessible until the firt 15 Colossi have been defeated)
G-1 Desert Fortress
G-2 Misty Falls
G-3 Half-Moon Canyon
G-4 Cliff Path
G-6 Valley Plain
G-8 Green Cape
H-6 Eastern Bluff
After defeating each Colossus, you are given an option to save at the Shrine of Worship. You can save there manually at a spot on the south side of the structure - I'm not certain if this is required for the trophy.