Finnish beliefs and customs varied greatly between different regions. Furthermore, cultural and spiritual beliefs have a tendency change over the course of centuries. Nevertheless, I would argue that the original Finnish belief concerning the afterlife was that the dead souls reside with their earthly remains and, thus, dwell near their graves.
It is commonly assumed in Finnic mythologies and folklore that each individual person has several souls. Moreover, each soul has a different fate after death. For the sake of brevity, I don’t touch the subject of the other souls here, but instead I try to represent few thoughts regarding the placement of the soul called itse, which can be equated with the “shadow soul” that houses the essential human consciousness.
There were several names for the afterlife destination of souls. There is vainajala, which simply means the place of the dead. Vainaja is the word for a deceased person and the -la suffix denotes “the place of”. Tuonela means the place of Tuoni, Tuoni being the personification of death. Manala probably comes from the words maan alla literally meaning “underground”. So all the names referring to afterlife locations simply refer to a place were the dead are and where Death is present. According to the old beliefs, the deceased soul didn’t go straight to the place of the Dead, but instead they had to travel across the dark river of Tuoni, albeit the souls received help on their journey from Tuonen tytti, i.e. the girl of Death, a Finnish Charon of sorts.
Curiously, the element of water is often connected to the afterlife beliefs. Many ancient burial places were located on islands, and Tuonela was also thought to be surrounded by dark waters. This might be a good example on how metapsyhical beliefs were juxtaposed with the characteristics of the local landscape. People might be buried six feet under in their local island burial ground, and in the mythic landscape of the community the souls were thought to reside in a otherwordly place that was also underground and surrounded by bodies of water.
The Sami people, and probably ancient Finns too, also have a concept of a abode for the Dead that is located in the sky. Strangely enough, this place, verisurman saaneiden vainajala (the place for those who have suffered blood-death), was only for people who were slayed in battle or who otherwise had met their end in this world by violent means. The reddish lights of the Aurora Borealis were thought represent the blood of these people, spilling from the eternal fighting that was still going on in the heavens. The connection to the Nordic beliefs of Valhalla is obvious.
However, the Finns apparently didn’t perceive this violent sky-abode a very desirable place to end up after death. The famous scholar Juho Pentikäinen recounts about one old saying that states that to go up after death (i.e. to the blood-vainajala in the sky) is a bad thing, but to go down (i.e. to Manala) is a good thing. Some people have speculated that the concept of sky-abode as an afterlife destination might have been introduced by the Scandinavians during their long trips to foreign countries (for reasons of trade and war).
Many of the Nordic explorers undoubtedly died on those journeys and it wasn’t always feasible to transport their corpses back to home. Burying their remains in foreign soil would have been a ghastly idea since they would have to continue their existence in their graves all alone and separated from their kin, community and homeland. So the travelers burned the bodies of their deceased fellows in order to free the soul from the body to find a new home in the skies. And thus the idea of the Viking Valhalla was born.
The Finns, however, seem to have thought that the best fate after death was to be buried in the soil of your homeland, next to your beloved kin, near the community. People were buried with the things they were thought to find useful in the afterlife. The dead souls continued their existence underground in the graveyard (i.e. Manala) where people came to pay them respects, ask for their guidance etc.
The Dead knew many secrets that the living were forbidden to know, so the noita sometimes fell into trance and traveled beyond our reality to fetch useful information from the dead to help the community. In our myths many Gods also frequently travel between these realities. The death and rebirth of Lemminkäinen at the Tuonela river is probably the most well-known example of these myths, famously depicted by Akseli Gallen-Kallela.
In ancient Finnish thinking the family was thought as a one unit, consisting of both the dead and the living members. The Dead are keepers of the traditions and virtues of the families and tribes. If the Dead were properly venerated, a stream of luck flowed from the underworld to the life of the living, bringing people wisdom and prosperity. Ancestors were protectors and guides of their descendants. During the yearly feasts the Dead were ritually commemorated. In addition, certain souls or certain parts of souls (i.e. individual characteristics) were thought to born again to the same family lineage.