Lara Croft and the Guardian of Light

In the first level, the Red Skulls are in the following places:
1. The first Red Skull is in one of the urns where the game teaches you how to attack.
2. The second Red Skull is in plain sight once you reach the 3rd area.
3. The 3rd Red Skull is after the healing point, when you have to type-rope walk with Totec, it is over the other side.
4. The 4th Red Skull, after you open a door in the 5th area, you have to spear jump with Lara onto a higher ledge, it is along that ledge.
5. The 5th Red Skull is in the 6th area, when you climb up the ladder to get the two big balls, it is in plain sight within the arrow range. Just blow up the arrow-shooters and grab it.
6. The 6th Red Skull (and also the Overachiever achievement) is in the 7th area. There are 7 pots on the floor, if you jump across them all without touching the floor, you will see the Red Skull on the one in the middle.
7. This one is just after defeating the Flame Trap. It is to the right as you walk out.
8. No.8 is in the same room as no.7. After you cross the gap, get Totec to throw his spear into the wall to the left of the exit door. You might need to throw more than one to get some height for Lara to jump on it, and reach the Red Skull above.
9. No.9 is in the next room. There is a hook on the wall in front of you, if you hook to it with Lara's rope (RB), you can wall run up to it. It's in plain sight.
10. The final Red Skull is in the room with the walls that move closer to you. It is right in front of you as you go to climb it, simply pick it up, and achievement unlocked.

Also, T Daddy3000 pointed out you may need to collect all the Red Skulls in more than one level before you get this.

For those of you that have glitched this and need the second level:
1. The first red skull is toward the bottom left (from character point of view) of the map of the first area. When you look at the map, its in a little curve in the wall at the bottom. You just need to jump to grab this.
2. The second Red Skull, you need to be Lara for. In that first area still, you come across some blown-up trucks. Behind them, is a broken wall. Get Totec to spear it or use his shield jump to get over the wall, and grab the Red Skull form under the tree.
3. On the bridge from the first area, the will be a statue of a man, holding the bridge. Simply Spear Jump up there to grab the skull.
4. (the next few are not necessarily in the order you will get them). If you go left from the temple, the forward a bit, you will come across a river. There is a Skull in the river.
5.Past the river, keep going left, you will see the Red Skull atop a pole. As Lara, stand atop Totec's shield, and do the 'Jump Jump' achievement (he jumps, you jump) to reach it.
6. After the previous Skull, jump down into the river, and walk around it till you reach a big ball, a switch, and some salamander type creatures. In the river near there, half submerged, is the next Skull.
7. If you walk toward the screen to the left from the last one, you will come across some big stairs. Down these stairs is a bonus room. To the side of the bonus room, the is a tilted pillar, run up it, and jump onto the roof to grab the next Red Skull.
8.In the top right most corner of the map, there is a Red Skull hidden in a tree (it's on ground level). This is just after the braking bridge event.
9.After defeating the temple thingy, keep going till you reach the bottom of the waterfall. There is a Red Skull atop the building in the waterfall (the Sun Disc Tomb Entrance). Use the 'Jump Jump' technique to reach it.
10. From the last one, walk toward the screen a little, it is a top a short platform... Least Hidden Secret Ever...

The first place you can get this achievement, is of course, level 1 Temple of Light. Below is a video to find all 10 in that level.

Thanks to RoosterTeeth