What are the locations of all the hidden/optional tombs

Once you reach a certain point in the game, you can freely travel around the campsites gathering any missed GPS caches, relics, documents, etc. In some of these areas, the Mountain Village specifically, there will be more enemies, as well as new, helpful objects appearing in your Survival Instincts.

More specifically, there are some grounding points for rope lines scattered about, generally with a direct line of sight on the roofs with the rope coils. You can fire a rope arrow into the roof, ground it to the pole, and enjoy some ease of travel around the once hard-to-travel Mountain Village.

Sadly, that seems to be the only use for those roofs. Minor, unnecessary rope-lines, and annoying golden glares in your Survival Instincts.

You need to get close to this opponent so that he swings his melee weapon at you.

When this happens scramble out of the way (Shift on PC w/ keyboard, B on Xbox controller or O on the PS3), this will leave him exposed and stationary for a short period of time, now is the moment to attack the target.

After a short time he will raise the shield again, so you might have to repeat this pattern a few times (if I remember correctly this first shield guy is also wearing armour, so requires more time than others that come later).

Later in the game you can obtain other options that make shield guys easier to deal with (counter melee attack built in to a scrambling-dodge, for example), but the basic strategy is the same - get close, force them to expose them self, counter attack.