I am absolutely certain that an afterlife exists although I don't claim to know what it will be like.
I believe it will be a spiritual world, not a physical one, and that we will have a spiritual body, not a physical body, but that is about all I know.
I believe there will be no time as we experience time in this world, and we will still have work to do. I am glad for that but I cannot imagine living forever and being bored!
“Those who have passed on through death, have a sphere of their own. It is not removed from ours; their work, the work of the Kingdom, is ours; but it is sanctified from what we call ‘time and place.’ Time with us is measured by the sun. When there is no more sunrise, and no more sunset, that kind of time does not exist for man. Those who have ascended have different attributes from those who are still on earth, yet there is no real separation.”
‘Abdu’l-Bahá in London, pp. 95-96