If you want all the Armigers in the game, then you need to pay a visit to Malmalam Thicket for Tomb of the Pious and Myrlwood Forest for Tomb of the Rogue.
Both are recommended to be tackled when you have levels in the mid to late 30s, and when you're done, be sure to check out other Final Fantasy 15 dungeons and tombs for more places to explore.
Malmalam Thicket (Tomb of the Pious)
Recommended level: 35
Malmalam Thicket is locate in the south west area of the map - take the road west from Old Lestallum, turn south at the end of the road, and park just north of Maidenwater. Make your way on foot (or chocobo) through the woods until you locate the entrance.
The dungeon itself is a straight run from entrance to goal. You'll face off against pockets of Soldier Wasps (weak to Javelins, Daggers, and Ice, resistant to Lightning) and Mandrakes (weak to Swords, Guns, and Fire, resistant to Lightning) on your way, and when you reach the open area at the end you'll be fighting a Bandersnatch.
It's weak to Javelins, Mechanisms, and Lightning, and resistant to Fire, and the fight takes place in a nice open area which provides plenty of opportunities to make long-distance Warp Strikes to take big chunks of HP away from it.
When he's down enter the tomb to collect the Scepter of the Pious.
Need more help? Our Final Fantasy 15 guide and walkthrough can provide tips on main story, as well as the open-world's many quests and activities. Learning how to get AP fast, EXP fast and money or Gil fast will aid you in many optional dungeons and tombs - including how to open and explore their locked doors. There's also plenty of interesting side-quests, too, such as the Scraps of Mystery and Professors Protege frog locations. And if you want to get around easier, you can rent a Chocobo, learn the infinite sprint trick and later in the game, get the flying car Regalia Type F. There's also more to see and do with DLC, such as Episode Gladiolus and Episode Prompto.
Myrlwood Forest (Tomb of the Rogue)
Recommended level: 36
The Myrlwood is in the north west corner of the map, just south west of the Vesperpool. Make your way along the wooded path to the entrance, and head more or less straight west through the forested area where you'll find a few Mushussu (weak to Javelins, Shields, and Frost, and resistant to Fire) and Mandrakes.
Once you're through the woods you can take a left turn to find a campsite, fishing spot, and some Elemental Essences, and the other route will lead you to the Treant. He's weak to Broadswords, Mechanisms, and Fire, and resistant to Lightning, but there's no real strategy available here - just whack him until he's dead.
Once it's safe, enter the tomb to collect the Star of the Rogue.
Tomb of the Just location
This is by far the simplest (optional!) TombHead for the Secullam Pass parking spot (between Saxham and Secullam Pass) in west Duscae, and follow the path west, and the tomb is at the end. No dungeon, no monsters, no drama. Easy!