Two words cubone's mom.Also Lavender towns tower is scary.
I wasn't scared of Cubone's mom but rather the Gastly's prior to obtaining the Silph Scope. Also I think the Champion battle theme creeped me out too.
But what the ladies in the tower said is to morbid.
OMFG yes, I was too young before to even know what they were getting at but my goodness looking back, that place is more creepy than ever. Pokemon: Children's game or mental scarring for life? You decide!