I remember listening to this serial in the late 80's. It was really well written. At one point they come to a pyramid and have to enter it by solving problems. I think this might have been a bbc serial, but i'm not sure
This sounds like Earthsearch by James Follett, first broadcast on BBC Radio 4 in 1981/1982, but maybe repeated later.
There's a tiny group of young people on a spaceship, their lives run by computers:
From infancy, the four third-generation crew members (now in their early twenties) have been raised by robots and by the Angels – mysterious unseen beings who run the ship and who only manifest as disembodied voices. [...] the ruthless, manipulative control of the Challenger's megalomaniacal control computers, Angel One and Angel Two.
And there's a huge structure that they need to solve a puzzle to get into:
The only sign of life is a huge ten-mile-high tower on the equator, with a tiny village nearby. [...] The crew examine the tower, finding that there is a door set into one side which cannot be opened. Peeron says that many of his predecessors have made attempts over the centuries – for example, by hitting the door with battering rams – but it will not budge. It is said that it is held shut by a "lock of knowledge". Darv eventually works out how to open the ingeniously simple lock, which requires a low grade of technology which would only be available to people who have already worked out basic principles of science and engineering.
(Quotes from the Wikipedia article.)