Scribbling in the Depths is an achievement that requires the player to obtain the Constitution experience after completion of the Song from the Depths quest with level 80 Constitution.
Enter the quest cave (entrance in a wall south of the Rimmington mining site). Swim through the acid pool (requires 50 ) and go through the only door to the east. In the next cave, go west, then south, then east, then north. Read the northern Ancient writings for 5,000 experience, then swim through the acid pool (requires 80 and will cause 50+ damage, but cannot kill you) and read the second wall for the remaining 25,000 experience. Before reading the ancient writings, their examine text is, "This text is some kind of magic to fortify the body." Once the ancient writings have been read examine will yield the message "The writing has jumbled to become incomprehensible."