Uncharted 4 has a variety of collectibles hidden in each level. In addition to the normal collectibles, there are some secret items that are also hidden through some of the chapters. These are mostly easter eggs that reference the past games developed by Naughty Dog.
There are a grand total of 3 different strange items to be found in the game.
Strange Pendant: This can be found in Chapter 9. After solving the puzzle that requires rotating a water bucket and crucifixes, jump down the cliff on the right side. You will be able to attack your rope to swing to a platform with a skeleton holding this pendant.
Strange Relic: This can be found in Chpater 12. Once you follow all the arrows on the tiny islands, you will reach a location where Sam will split up with Nate because one of the rope bridge will break midway. After reaching an old tower on the top of the island, you must use your rope to slide down some mud. Go left and you will see a small hill that you can climb. From that hill, you will have to make a faraway jump into the abyss and make sure to attach your rope at the last second, which will result in you swinging to a platform with this strange relic in the bowl.
Strange Fruit: This fruit can be found in Chapter 21 inside the cave near the end of the mission. After attaching your rope to a wooden structure, swing down to see the Avery’s pirate ship in the water below. You will be able to to spot a cave entrance in front of you on the ride side. This cave is pretty far away and can be missed in a jump but once you manage to reach it, you will find the strange fruit there.
Uncharted 4: A Thief’s End is available now exclusively for the PS4.