4th Singularity London: Southwark free quest is the best AP & time-saving location to farm Homunculus Baby. You'll get about 3x Homunculus Baby by spending 190AP. Evil Bone is also dropped.
Here is a list of servants that need Homunculus Baby to perform Ascension and Skill Up.
Rashoumon event (Ibaraki Douji event)
Murder at the Kogetsukan
Inheritance of Glory
5 Star Servants Tier List: Best Servants [5/9 updated!]
FGO Reroll Tier List [5/11 updated!]
How to farm EXP cards & level fast
Device Transfer Guide
Best Servants [★4]: 4 Star Tier List
Anastasia Nikolaevna Romanova
Ivan the Terrible (Ivan the Thunder Emperor)
Talk on the Heated Sands
Holy Night Supper
Lunar Hot Springs