Sometimes, quite by chance, building work reveals a new vista on an imposing piece of architecture.
Take the demolition of some non-descript modern accommodation blocks on that part of the Whittington hospital grounds fronting Dartmouth Park Hill.
It has revealed the majesty of the oldest part of what is now the Whittington hospital - the splendidly Italianate, 170-year-old Smallpox and Vaccination Hospital, built to serve a purpose which, sadly, has such a contemporary ring to it.
It takes us back to another era when vaccination was a burning issue and a public health necessity.
More than 200 years ago, an English physician, Edward Jenner, established the effectiveness of a vaccine against smallpox - though there had been earlier initiatives in Turkey and China. And in the 1850s inoculation became required for infants in England and Wales.
Some strains of smallpox killed one-in-five of those who caught it - and scarred and disfigured many of the survivors.
The global eradication of this disease in the 1970s - along with rinderpest, smallpox is the only infectious disease to have been completely banished (outside the laboratory, that is) - has been one of the great triumphs of public health.
The isolation and vaccination hospital built on what was then a green field site from 1848 replaced an older institution demolished to make for the building of the Great Northern Railway's London terminus at King's Cross.
In the mid-nineteenth century, the medical approach to smallpox was to quarantine those who showed signs of inflection and to inoculate those who may have been exposed - in what might be called a forerunner of test-and-trace, though quite a lot cheaper.
Mass vaccination was carried out to limit serious outbreaks. Although the inoculation of infants in England and Wales was supposedly compulsory, compliance was far from complete and from 1907 conscientious objection to being jabbed was permitted. The policy of vaccinating infants against smallpox continued into the 1960s.
The view opened up from Dartmouth Park Hill is of a grand facade rather grievously disfigured by a fire escape. But unfortunate as this intrusion is, don't fume and fret too much. This is just the west-facing flank of the building.
The main facade, looking south, is altogether grander, with portico, clock and inscription, though it's hemmed in by later buildings in a manner which disguises its architectural ambition.
The architect, Samuel Daukes, was prolific - churches, stations, hospitals, stately homes, hotels, warehouses, whatever - and undiscriminating, in as much as he was happy to design in any suitable style.
While working on the Vaccination Hospital he was also knocking into shape an even more imposing medical institution, the vast Colney Hatch Lunatic Asylum (later Friern Hospital and remodelled in the 1990s as private housing).
This is also Italianate in appearance and once boasted - though how exactly this was established is anyone's guess - the longest corridor in Europe.
Daukes has another enduring connection to Highgate - he's buried in the family vault in the old part of Highgate cemetery, barely a bedpan's throw from the Whittington's wards.
Isolation hospitals are usually built in the farther reaches of a city, and as the urban area expands these institutions stay on the outer ring.
By the end of the nineteenth century, the isolation wards had moved to South Mimms in Hertfordshire. The Islington Union Infirmary was built directly to the south of the Vaccination Hospital - and the older building was reduced to serving as the administration block.
In time the Islington Infirmary merged with the adjoining St Pancras and Holborn and Finsbury infirmaries , and the three-into-one hospital took the name Whittington at the inception of the National Health Service in 1948.
The NHS is the most cherished of public institutions - but in one aspect, it has failed to live up to the jumble of health provision of an earlier age.
It's difficult to think of a modern hospital quite as compelling in design as the building which now catches the eye from Dartmouth Park Hill.
- Andrew Whitehead is a local resident and historian and author of the 'Curious' series of books about North London's past.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here