Most of the earliest sea level data records come from commercial or military ports. Having a record of the tide was important for ship navigation. Sea level records were also important tools in the establishment of a national datum, or zero level, to which heights on maps would be referred.
Some of the earliest tide gauges (which have given us some of longest sea level records in the world) were housed in specially designed huts. Because of their age, a lot of these buildings are of unique and interesting design. Below are a few examples.
“The Kronstadt sea-gauge with the tide gauge pavilion is a zero-level of the Baltic system depths and heights. All depths and altitudes (even the heights of the flight spacecraft) in Russia and some other countries (former Russian Empire) are measured from the level of Kronstadt sea gauge. Yuri Gagarin, the first spaceman in the World, ironically said in 1967 that this is it the Hub of the Universe.”
The sea level has been measured at Kronstadt (although not always at the same location) since 1777, making it one of longest sea level records in the world.
Some more tide gauge buildings:
The Tidal Observatory was established to determine the mean sea level used as the starting point for levelling in the UK. A brass bolt on the site is the benchmark for the whole of the United Kingdom. All Ordnance Survey map heights are referenced to this point.
The height of the benchmark was established over a six-year period from 1915 to 1921. Visual observations of water level on a tide staff were made every 15 minutes, 24 hours a day, 365 days a year. From the data collected over this period, mean sea level was caculated and this vertical level marked with the bolt.