Saints Row: The Third Remastered

MINOR MISSION SPOILERS

Buy the Collectables Locator for your map like the other solutions say, but to make this achievement come most easily, I suggest travelling to each collectable location with the Specter (Hover Bike), which you have the option of unlocking on the mission "My Name is Cyrus Temple".

During that mission you choose two prototypes to sign off on (Specter, improved Tank, and satchel charges).

Make sure you choose the Specter as one of the two because it is as fast as any flying vehicle, allowing you to get around the various locations like rooftops and caves quickly and easily, but also durable and small enough to make it an easy vehicle to land, compared to the VTOL or a chopper. Using the Specter and the Collectables locator map, this achievement takes about 45 minutes to an hour.

There are 80 Collectables to obtain (20 blow-up dolls 20 cash palettes, 20 drug palettes, and 20 photo ops) and most of them are easy to get to. Only a few times did I have to even get off the Specter because you can drive over them to pick them up.

A few of them are inside caves or buildings, and others are on roofs, but believe me, there is no simpler solution than travelling via the Specter.

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ive seen in the comments ( credit goes to @shadowsniping ) not all collectables show up on the map and in order to find the rest you need to filter them on the map to just the collectables and they should show up for you. thank you for the constructive comments!

I would advise getting the collectible finder upgrade in abilities which unlocks at level 20 before doing this as it will make finding them while using the map easier, though it is unnecessary, and using the Salem vehicle(should be available from the start from the main crib) as it is very maneuverable and makes this go faster. See the map near the top in the link for locations (click on the map to expand it). https://saintsrow.fandom.com/wiki/Collectibles