Sometimes one stumbles on a parallel universe.
Perhaps in a newsagents. A magazine, hastily bought for a long journey, turns out to be a revelation. It shows you that heritage is not just another name for the built environment. From here on in you know that heritage is in the air.
All over the developed world, it seems that nostalgia is sprouting full-size wings and time is being made to stand still by amateur aeroplane builders working from copies of ancient sets of plans bought on the Internet.
For instance, did you know that right now in America, a small aircraft company is building five replica Messerschmitt 262s, copies of a German jet fighter that became extinct 57 years ago and is now to be brought back to life? Did you know that in New Zealand, a man is patiently making his own set of machine tools so he can use them to make a fuselage for a replica de Havilland Mosquito that many years from now may take to the air?
In Norway, parts of a Gloster Gladiator biplane fighter that crashed into a mountain in 1940 have been scooped up and shipped to England, where they will be mated to a newly built replica fuselage and a set of wings from another wrecked Gladiator. In time this compilation will emerge as an aeroplane in authentic Norwegian markings, bearing the serial number of the aircraft that originally had the wings.
When this is done, there will be three Gladiators that have been brought back to life, or 'restored to airworthiness', on the civil aircraft register. Exultantly, they will be photographed flying in formation 1930s style and eventually, one by one, they will either crash and be recycled again or become exhibits in the world's burgeoning number of aviation museums, of which there are more than 70 in the UK alone.
Once you become interested in this consumption of the obsolete, you can find out more. Marvelling at the '10,000 hours' that have already gone into the restoration of a huge Douglas Cargomaster transport plane (due to be finished this year), you will finally come to the biggest aviation preservation project of all - the proposed purchase and repatriation from Rio de Janiero of the Brazilian aircraft carrier Minas Gerais (formerly the British Second World War aircraft carrier Vengeance), and its restoration to HMS Belfast levels of authenticity as a floating naval aviation heritage museum anchored in Southampton Water.
Compared with these death or glory exploits in the cause of aerial conservation and preservation - most people only hear about restored aircraft when they crash at air shows - the issues confronting the almost fully institutionalised conservation wing of the architectural profession seem mild indeed.
Aero-conservationists search the world for wrecked aircraft, one month bargaining with Siberian peasants for what is left of a crashed German bomber, the next, cutting a fiveinto-one 'composite rebuild' deal in Australia for the veritable phoenix of the Brewster Buffalo.
Nor, when they get their wrecks to their workshops, do they get much help from the original manufacturers, many of whom no longer exist, and even those that do are unwilling to release the construction drawings filed for their long-expired certificates of airworthiness in case they get sued when they crash.
Of course, being mass-production items, nearly all these crash rebuilds once existed in some numbers, but then they equally often failed to leave their bones in the right place for preservation - which is apparently the bottom of a frozen lake. A place generally not on the beat of the conservation officer employed by the council.