The main entrance is found by investigating the statue of King Rada I in the center of the city. The fastest way to get to the catacombs is by kourend teleport which can be obtain in arceus Library with a book called teleport of incarnations or you can teleport using the xeric talisman with the teleport xeric heart!
With this map it will show you general direction of each NPC/Monster with the new update the map may change for more of the particular NPC/Monster like hill giants will become Velds and Greater Demons into Abby demons. This dungeon is great for the maximum experience and cash per task but yet does take longer specially to lower levels. Catacombs is consider the second best to burst, but be sure to keep your prayer up! Hope this Guide Helps.
Note* You can kill Scatizo in this dungeon by obtaining a full totem which can be obtain from the Monsters inside this dungeon and you can also charge your Arclight with 3 shards or add more for 1k attack a piece same as the totem can be obtained by Monsters/Npc within the dungeon!