Jesus on the Cross
Jesus Christ was executed on a wooden cross, and three days later he rose from the dead to appear in front of many witnesses. Although life after death was believed by nearly every human culture (including our own) until recent times, modern culture tells us this is impossible.
People who saw, spoke to, and physically touched the resurrected Jesus went on to spend the rest of their lives spreading his message — the good news (called the gospel). That by following Jesus we're put right with God, and saved.
They did this despite massive opposition from their own culture and from the pagan culture of the Roman Empire. Most of them ended up being executed themselves for refusing to deny that Jesus was their only Lord. These original disciples were actually there themselves, with Jesus, when it all happened. If Christianity was a fake, they certainly would have known. Because they were there and saw it with their own eyes. And if it was fake, why would they willingly choose shameful and torturous deaths by execution as criminals — just to recieve a supposed future reward that they knew to be nonexistent?
Sometimes people find it hard to accept that God would put his faithful servants (even his son) through such physical torment. But when you believe in the much bigger picture, this physical suffering is only tiny compared to the heavenly rewards that follow from it. The willing and violent deaths of the eyewitnesses to Jesus' resurrection prove to the rest of the world that they must have seen something real — in a way that no peaceful life of material success could ever have proven.