The Caves of the Dead - Opening Adventure

This could be slotted into any campaign or adventure.

You've travelled for a few days now and feel tired and weary. The wind and rain batters on your back, a storm is coming. The rain is so heavy it's making it hard to see, however squinting in the distance you notice a large cave. Holding your arms up to defend your face you slowly make towards the cave entrance. The wind is blasting against you, trying to force you back, or warn you, but you are determined to get to the entrance of the cave.

Finally, shelter. The interior of the cave is decorated with green mold patches covering the dripping walls. It's a dark sort of rock and the cave floor moderately declines deeper. The rain has caused the floor to be wet, so it feels quite slippery.
Easy DC acrobatic check to see if they walk into the cave safely, if not then a moderate DC reflex check, upon fail a character slips down into the darkness and disappears from the rest of the party. If all party members fail this roll, they slip down the slope in darkness. They hit the bottom and take easy damage).

Descending to the bottom of the cave you enter complete darkness. A void surrounds you and a coldness envelopes you. You shiver and feel uneasy about this place. Pure silence greets you as the sounds of the bellowing storm fades to nothing from the outside. The only company is the sound of the party's breathing and the sound of a small drip coming somewhere nearby. Looking around with a light source the cave has suddenly got smaller and there are no other passage ways. It could be a good place to rest for the night.

(Players can rest here for the night, a passive perception check of a hard DC notices a small lever on the east side of the cave on the floor. Players can actively search the room for this with a hard DC. Upon failing them both, the party can rest or wait. If the party want to return upwards and out of the cave, they can do a moderate acrobatic check to get out of the cave).

If Sleeping
(Sleeping players need to make an easy DC passive perception check, however ignore this is there is one character on guard or meditating. Upon failure, the zombies grab the nearest player and gang up on him or her. See zombie grab in the monster manual)
(Character being grabbed) You feel a cold but strong grip on your arm, followed by many other grabs on various parts of your body. Your eyes snap open and through the sleepy haze you see a gang of zombies trying to rip apart your flesh.

If Waiting
The sounds of moans slowly but surely echo around the cave. The grinding sound of a rock can be heard, as if it's being slid across. Suddenly, the sounds of moaning and shuffling feet fill the cave with noise.

If Pulling on the lever
Pulling on the lever causes a nearby rock to suddenly jump to motion. It slides across revealing a new room to encounter. Peering into darkness you see dark humanoid figures slowly travelling towards you. It seems a group of zombies are hungry for some flesh!

(Regardless of how the players behave, it's a moderate EL).

With the last zombie slain the now open rock beckons for adventure...where does it lead?

From here onwards you're welcome to do what you want with it. Maybe it's an undead infestation? Or the lair of a Lich? Or maybe a necromancer's home who conducts experiments on corpses and tries to find ways to reanimate them.