Tower
It stayed in his nightmares. Every time he closed his eyes, he could see it all over again. The flash of green light, the dulling of blue eyes, the blackness of the night.
He kept seeing it.
Kept seeing Dumbledore falling, dead, from that tower. No matter how hard he tried, he couldn't get the image from his mind. It was a sight that would haunt him, as it should.
The death of the man who'd taken him in. The man who had become like a father to him over the years, not that he would ever admit that to the man or anyone else for that matter.
As Snape stood in the courtyard, eyes trained up on the errie looking astronomy tower, he wished beyond all measures that he had gone against the headmasters order. Maybe then he'd be alive. Maybe then Severus wouldn't feel like such filth.
But as the bustle of students entering the castle filled his ears, Snape turned his focus onwards. He had left Dumbledore with a promise to protect these students as he always had. And that promise hadn't ended in that tower.