There are many places you may have never heard of that serve as memento mori- a reminder that we are all mortal, and that not every culture buries their dead six feet underground. Here are eight of them.

Underwater Graveyard

Neptune Memorial Reef, three miles off Key Biscayne, Florida offers a final resting place for those who love the sea. Earthly remains are cremated, then mixed with cement and laid on the ocean floor with a memorial plaque. The cemetery lies 14 meters below the surface.

Hanging Coffins

The limestone cliffs over Sagada in the Philippines seem like an unlikely place for burial. In fact, many folks who died here were never buried, but are still in their coffins hanging from the cliff faces. The oldest coffin identified has been there over a hundred years, although the custom of placing coffins inÂ barely accessible places in the cliffs goes back a couple thousand years. Residents are more likely to be buried underground today.

The Fontanelle Cave Tombs

The Fontanelle Cemetery is located in underground caves in Naples, Italy. The former rock quarries were first used for burials in 1656 as a response to the overwhelming numbers of deaths from the plague. At times, up to 1,500 bodies were left per day! No graves were dug, but bodies were dusted with lime and forgotten. Centuries later, only bones remain. In the 20th century, Italians returned to the caves determined to give respect to the remains by "adopting" a skull. This is especially useful to widows whose husbands never returned from foreign wars in that they could mourn by proxy as they cared for another deceased, if nameless, person. Closed since 1969, the Fontanelle Cemetery has been restored and is now open to the public by reservation.

Colma Necropolis

When San Francisco passed an ordinance prohibiting any new cemeteries in 1900, burials moved to the area around the small town of Colma, California. In 1912, San Francisco began relocating its existing cemeteries to Colma. The town has 17 cemeteries for people and one for pets. The dead outnumber the living by a thousand to one! Colma has 1,500 residents and around 1.5 million graves. Image by Gregory Melle.

The City of the Dead

Dargavs, North Ossetia has a collection of 95 stone constructions known as the City of the Dead. Some are underground, other are above ground, and still others are a little of both. The buildings serve as mausoleums, with a building for each family. Some still contain remains of the dead. Very little is known of necropolis' origin, but it dates back at several centuries. Image by Dziadek Mroz.

The Skulls of St. Sebastian

St. Sebastian's Cemetery in Salzburg is the final resting place of some of Austria's biggest celebrities. Theophrastus Paracelsu, the "father of modern medicine" is interred at St. Sebastian, as well as Mozart's wife and father, and the controversial Archbishop Wolf Dietrich. St. Sebastian's, established in 1502, is adorned with skull motifs in every corner. Burials ceased in 1888. The cemetery is now open to the public daily. Image by Curious Expeditions.

Sedlec Ossuary

Sedlec Chapel near KutnÃ¡ Hora, Czech Republic has been a burial ground for nearly 900 years. In that time, thousands of bodies were laid to rest due to plague, war, and natural causes. Because there is not enough space for a grave for each one, the bones of earlier burials were dug up to make room for more. The Sedlec bone chapel, or ossuary, holds the remains of about 40,000 people. The bones were incorporated into the chapel as art and furnishings by FrantiÅ¡ek Rint in 1870. See a 1976 documentary tour of the chapel. Image by Curious Expeditions.

Capuchin Catacombs

The Capuchin Catacombs in Palermo, Italy are home to thousands of mummies on display. Embalmed corpses interred in the catacombs remained preserved better than other burial sites. This may be due to the particular pride Sicilian embalmers take in their art. Many of the corpses are arranged in tableaux that resemble scenes from life. Others are standing up in groups, as if posing for a picture. One of the more famous corpses in the Palermo catacombs is Rosalia Lombardo, who died in 1920 at age two, but whose body has not decomposed. The Capuchin Catacombs are open daily to the public.

See also: Destination Cemeteries.

Looking for smart gift ideas? In search of a new quirky t-shirt? Head over to the mental_floss store.