People usually call the souls or sprits of the dead, ghosts. After a poll done in 2005 about 32% of Americans believe in ghosts. Humans and ghosts have had a very interesting relationship. Actually ghosts have been a part of some cultures and holidays for years now. And some ghosts stories can be pretty historical.
Many cultures do festival to celebrate the dead either for respect or actually fear for ghosts. One of the most common is the Day of the Dead celebrated by Latin Americans. Other festivals that honor the dead are China's Hungry Ghosts festival, Japan's Bon Festival, and Nepal's Gai Jatra or Cow festival.
Another activity that connects humans and ghosts is ghost hunting. Where we the living go and look for the dead. Ghost hunting is usually done with a group at night at a historical site. Researching about the site would be very helpful for a better and funner ghost hunt. Some sites even give ghost tours. Some examples are the Queen Mary, St. Augustine lighthouse, and Winchester Mansion.