"And under here, Hedwig - [...] - is where I used to sleep! You never knew me then - blimey, it's small, I'd forgotten..." -- Harry Potter
On the ground floor of 4 Privet Drive, there is a cupboard under the stairs; this was Harry Potter’s bedroom for about 10 years. The cupboard is very small, containing only a bed. It is always full of spiders (PS2). The Dursleys often punished Harry by locking him in his cupboard for days. After Harry’s first Hogwarts letter arrived, Vernon burned it, but he allowed Harry to move from the cupboard into Dudley’s second bedroom, as a kind of compensation. The Dursleys locked Harry’s school things in the cupboard after Harry’s first year at Hogwarts, so Harry couldn’t access them during the summer. When Harry visited his cupboard for the last time in 1997, he saw that it was then used by the Dursleys to store shoes and umbrellas (DH3).
"Harry was used to spiders, because the cupboard under the stairs was full of them, and that was where he slept" (PS2).
"Perhaps it had something to do with living in a dark cupboard, but Harry had always been small and skinny for his age" (PS2).