But now, there it is, Britain's newest theatre, one of the last to be built this century, at a cost of some pounds 6m, and the first of the new century, in the sense that it's about the first of our millennium projects to have opened - and bang on time.
MoT? Doesn't that mean a transport test, for cars and vehicles and stuff? Precisely, for that's what it was for over 20 years, a unique mobile theatre, known and loved and remembered by thousands of people all over the country, from Carlisle to Guildford, and at the same time cursed by thousands of motorists unlucky enough to be stuck behind it as it trundled around the country.
The Century Theatre, as it was then known, first set out from Hinckley, Leicestershire, in 1952. The tradition of travelling theatre had, of course, been established for centuries, with groups of players touring the country, putting on plays in local venues. In the post-war years, however, theatres were hard to find, local halls often ramshackle, digs appalling, so it was decided that this would be a proper travelling theatre, carrying everything.
Its creation was a miracle of engineering and ingenuity - a caravanserai of 23 monster vehicles, tractors and trailers which contained living quarters for up to 20 cast and crew, complete with kitchens and lavatories, a scenery van, workshop, booking hall, office, facilities for printing programmes and their own newspaper, a generating plant, a lavatory for the audience and the bits and pieces for a real theatre. When they arrived, unpacked and set up - which normally took eight hours, depending on wind and rain, and the terrain - they had transferred themselves into a fully equipped theatre with a proper stage and seating for 225. Everyone, star or sparks, got the same - pounds 2 a week.
For more than 20 years, they moved on, every two weeks, packing up and travelling on a Sunday. That was the day not to get stuck behind them. You had little chance of overtaking the enormous convoy in the years before motorways.
The Daily Worker (today's Morning Star) praised the democracy, and the theatre world of the Fifties thought it divine. The original supporters and subscribers included Laurence Olivier, John Mills, Dame Sybil Thorndike, Terence Rattigan, Michael Redgrave, and Ronald Colman. George Bernard Shaw refused to contribute: he maintained that he had donated quite enough to the theatre with his talent.
In more recent years, people who have acted or worked in the Century Theatre, while still relative unknowns, include Bob Hoskins, Tom Courtney, Helen Mirren and Henry Livings.
The theatre always came to Keswick in the summer season, from 1961 onwards, plonking itself down on a prime site beside Derwentwater. This was where it finally came to rest in 1975, the curtain coming down on its travelling days, the end of a theatrical career for the hydraulic jacks and the former RAF 30hp Crossley tractors which had been so cleverly converted. In a word, it was knackered.
It remained stationary, on the site, becoming The Blue Box, still showing live theatre in the tourist season. I took my family there every summer from the early Eighties onwards, usually to watch an Alan Ayckbourn. Becoming a regular meant that I was always very careful not to book a seat in Row F: that was where the roof let in the rain.
From almost the moment it came to a halt, several local worthies began dreaming of creating a proper structure on the same site. Naturally, some equally worthy locals said no, and certainly not on that site.
It is one of the most beautiful situations in all Lakeland, right beside the little piers and the pretty steamers, which don't actually steam, more chug and rattle. A few hundred yards away is Friar's Crag and the monument to Canon Hardwicke Rawnsley, the Keswick vicar who was one of the founders of the National Trust. So it's not just a pretty site, a sacred site.
Battles had to be fought, sails trimmed, plans altered, before arguments were won. Then, of course, there was the money. How could a little town of only 5,000, known for its B&Bs rather than its millionaires, ever get the funding? Then along came the National Lottery. More battles and form fillings. About pounds 5m of the cost has come through Arts Council lottery money - while another pounds 1m had to be raised locally.
The two main activists have been Vicky Robinson and Graham Lamont, joint chairmen of the theatre. One is a hotelier, the other an accountant, and both have worked voluntarily for nearly 20 years. The presidents are Dame Judy Dench and her husband Michael Williams.
I went round the site on the morning of the opening with Vicky Robinson. It seemed surprisingly unchaotic, everything in place, except the name - Theatre by the Lake - which is to go above the entrance and hadn't been put up yet due to the usual planning permission delays. The National Park people can be beggars, as I know, telling you what colour of slates to use, when to pull your lavatory chain. I made that up, but they were jolly beastly to Melvyn Bragg over his conservatory.
"We like to think it's a state-of-the-art theatre inside," said Robinson, "in a traditional setting, which will be for the whole community, available all the year round, not just as a theatre." The main auditorium holds 400 seats, plus 80 in a studio theatre. Then there are exhibition spaces, conference facilities, a coffee shop and a bar. There are lifts and facilities, not just for disabled members of the audience, but for disabled workers.
The outside is of Lakeland stone, under a Burlington slate roof, quarried in Cumbria and reflecting the slopes and shapes of the fells behind. Swallows are already nesting and there have been visits from deer, badgers and red squirrels. Plus, of course, a full house on Thursday night. Le tout Keswick was there. I don't think that I've seen so many ladies in nice frocks and chaps in light but rather tightish suits in one place in Lakeland.
The plays in the opening season include The Lakers, an 18th-century skit on Lakeland tourists which has never been performed before, and the highly modern Two by Jim Cartwright, author of Little Voice. For the opening night, the frocks and suits were delighted by Charley's Aunt and did they all chortle at "Brazil - where the nuts come from" - surely one of the best known, yet totally banal lines in British popular theatre. It did creak a bit, but then it was first produced in 1892. However, no one inside what is a truly handsome and attractive and worthy theatre got wet...
Theatre by the Lake, Lakeside, Keswick, Cumbria, CA12 5W. Tickets and information: 017687 74411. The three plays mentioned run in rep till November, followed by performances by local groups. At Christmas the resident company is performing `A Christmas Carol'