There are 3 Hidden Achievements in the Exploration Catergory of Ruhnuk, Tineback Tamer, Leg Day & Wraid Night.
While no Combat is required for Leg Day or Tineback Tamer, you can get attacked so bringing a Level 80 character is a good idea.

All images in this guide have a Click to Enlarge Option.

Leg Day

This is the easiest Secret Achievement. All you need to do is run up the Mandalore’s Encampment staircase and jump off the top over and over and over without dying until you earn the Achievement: Leg Day.

Start at the Bottom of the Staircase at Mandalore’s Encampment, make sure your Companion is set to heals because if you are too slow the achievement may not complete.

Once you get up to the top of the Stairs, let your companion heal you until you get to around 80% HP or more, then climb over the railing NEXT to the boxes and jump down, aiming to land on the Trash head or metal floor at the Bottom.
NOTE: Dying to fall damage, hitting or landing on the staircase on the way down may reset the achievement and you might have to start again.

You need to just keep doing this over and over and over until you run back up the top and the achievement grants. It took me about 5-10 runs in a row without dying before the Achievement: Leg Day was given.

Tineback Tamer

This Hidden Achievement involves finding 3 Overripe Lambro Cactus you can click. They are sparsely placed around all of Ruhnuk and are not highlighted Blue. This means that you have to manually hover your cursor over each one to check if it is OverRipe.
The OverRipe Lambro model is a small, fat Green Lambro with a small orange tuft of flowers at the top, with 2 small Green Lambro balls on either side.
Upon clicking, the Lambro will Despawn and apply a special Buff called Intriguing Scent to your character that lasts for 10 minutes. You have to find 2 more OverRipe Lambro’s before time runs out. The Lambro will also give you Pet Baby Tineback that follows you, it only has 50k HP and Hostile Creature and Hidden Chain mobs will attack and kill it if you aren’t careful.

If you change instance, die, leave the planet, the Buff time runs out OR the Baby Tinebacks all die before you find 3 OverRipe Lambro’s, you must Restart.

When an OverRipe Lambro is clicked, it changes where it Respawns after around 30 minutes, I highly suggest going to each of these locations and finding 3 Spawned Lambro before attempting this Achievement. Remember that a Lambro will only Spawn at a Star of one color, so you must go around Ruhnuk and Click on 3 Different Lambro Spawns.

Each image above shows an OverRipe Lambro and its possible Spawn Locations:
Lambro One (Orange) – Hollow Chasm Map
Lambro Two (Yellow) – West Side of Overgrown Mining Site
Lambro Three (Pink) – East Side of Overgrown Mining Site
Lambro Four (Green) – Verdant Ravine or the Dilapidated Waterworks

Once you have collected both items, head into the Beast Pit via either the top or bottom tunnels (pictured below), you are now ready to fight the secret Ruhnuk Wraid Boss! It can easily be done as a duo with healer companions or in a group of four with one player as a healer,
but a large Operations group won’t hurt either.

Once you click the slab with the items in your inventory or with a groupmate nearby with one of the two items. They will both be consumed and several groups of Wraids will spawn in the arena, you should be able to kill them easily. Once they have tied the Wraidboss known as Tiroxe, Once-Slumbering will spawn with approx 7.6 million HP and familiar mechanics to the Wraid worldboss Trapjaw on Tatooine.

Once you have defeated Tiroxe, the Pheremones and Dewback Corpse in your inventory will be deleted and all group members present in killing Tiroxe will be rewarded the Wraid Night achievement and Legacy Title: Wraid Boss!

Credits: Guide by TodayinTOR, thanks to LordofTransform, Emi’thiss, Swtorista, Ynyss and about 10 random people on Ruhnuk that helped me find all of this stuff.