The air had grown chill the minute they descended into the strange valley, which was unmarked on any of their maps. It was so strange here, devoid of animal life and completely silent. The horses were nervous the entire journey through the vale. As they set about to collect firewood for the campfire they could hear their own voices as dim echoes through the eerie silence.
The food didn't taste anything that evening and their sleep was cold and troubled by nightmares. While they are clearing camp the next morning, one of them stumbles over a piece of stone jutting out of the ground nearby the horses. On closer inspection there seems to be runes engraved into the polished surface. The symbols true meaning is no more known among mere mortals and if they decide to dig deeper, they will discover that it is an ancient altar buried within the soil.
Any historically oriented party member will recognize the largest symbol to be the insignia of the powerful warlock who ruled this realm several centuries ago. At their departure from the area, something will seem amiss with one of the party members and all will remember the stories of the warlock's thousand curses.
I once read a book about a group of people who discovered a hidden temple city in a mountain range, where the Incas-the ancient civilisation of Peru- had fled to when the spanish invaded. When this group found the burial chamber of one of the inca high priests, they unleashed a powerful curse upon them all...