He ascended into heaven

He ascended into heaven, and sits at the right hand of God the Father Almighty.
- The Apostles' Creed

Commenting on this line here's J.I. Packer's typically concise explanation of what Heaven means in the Bible. No, it's not the place in the clouds where we don togas and play golden harps, it's something much much grander.

"Heaven" in the Bible means three things: 1. The endless, self-sustaining life of God. In this sense, God always dwelt "in heaven," even when there was no earth. 2. The state of angels or men as they share the life of God, whether in foretaste now or in fullness hereafter. In this sense, the Christian's reward, treasure, and inheritance are all "in heaven" and heaven is shorthand for the Christian's final hope. 3. The sky, which, being above us and more like infinity than anything else we know, is an emblem in space and time of God's eternal life, just as the rainbow is an emblem of his everlasting covenant.

Packer goes on to explain which meaning applies to how the gospel writers described Jesus' ascension (see Mark 16:19, Luke 24:51, Acts 1:1-11).

What happened at the Ascension, then, was not that Jesus became a spaceman, but that his disciples were shown a sign, just as at the Transfiguration. . . . Jesus' final withdrawal from human sight, to rule till he returns in judgment, was presented to the disciples' outward eyes as a going up into heaven in sense 3. This should not puzzle us. Withdrawal had to take place somehow, and going up, down, or sideways, failing to appear or suddenly vanishing were the only possible ways.

Above quotes taken from Growing in Christ (pp. 63 & 64)