Ankrahmun Pharoah Tomb discovery points are located in every Pharoah tomb not just "Horestis Tomb"
MAKE SURE TO BRING SCARAB COINS (10) just in case you mess up.
Also GFBS are advised if you want bestiary.
I recommend starting at "Omruc" (Peninsula Tomb). Working your way clock wise.
(Important) Make sure you go through every single floor in all the tombs.

Then working your way to "Horestis Tomb". This is also where you click on your map to start discovering.

Next go to "Rahemos Tomb" (Oasis Tomb).

After that travel north to "Dipthrah Tomb"(Mountain Tomb).

Once finished travel east to "Vashresamun" (Ancient Ruins Tomb).

Once complete travel south to "Morguthis Tomb"(Tarpits Tomb).

Next travel a short distance south east to "Thalas Tomb"(Stone Tomb).

Next Travel south to "Mahrdis Tomb" (Shadow tomb)

Any additional information can be found on tibia.wikia.com
https://tibia.fandom.com/wiki/The_Ancient_Tombs_Quest/Spoiler
Once complete with all of Ankrahmun you also will receive a achievement.

Hope this helps.