Standing on the top of Lincoln Castle’s Observation Tower, I held on tight out of fear I’d fall off the narrow, circular viewing platform.

It’s windy up there, but an unexpected hazard was all the children running around pretending to be guards patrolling behind the crenellations.

Along the castle’s brand new walkway all around the boundary walls, more kids played at being archers firing arrows through slitted windows or just ran ahead to explore while their parents strolled more sedately behind.

There’s a reason why so many people were jostling for space up there: Lincoln is celebrating a historic anniversary.

It is 800 years since King John placed his seal on Magna Carta, the document credited with planting the seeds of democacy in the country – and Lincoln has one of just four surviving copies.

Back in 1215, 25 barons rebelling against the tyranny of King John forced the monarch to agree to a charter of rights that prevented him imprisoning men or imposing fresh taxes without legal cause.

While British legislation has come a long way since then, and only a few clauses from the original document remain enshrined in law today, Magna Carta is still a vital part of the country’s history.

Lincoln, which was an important city at the time, has wholeheartedly embraced the occasion and the Norman castle reopened earlier this month following a decade-long, €31 million revamp.

Straddling the top of the city’s hill, from the castle visitors can enjoy panoramic views of the flat county stretching away below.

Only the impressive Gothic cathedral directly opposite – which was the tallest building in the world for almost 300 years before an earthquake toppled its spire – can rival this viewpoint.

To allow access around the full distance of the castle walls for the first time, several bits have been reconstructed or spanned over with bridges.

Colourful bunting flags flap in the wind to show the way and an optional audio tour explains more about withstanding invasions.

The main draw of the revamp is the vellum Magna Carta itself, which is displayed within a special underground vault alongside a copy of the Charter of the Forest, which was issued to deal with land rights in 1217, and a letter from the king still bearing his seal dating from 1213.

King John later repealed Magna Carta but it was reissued by his son and successor King Henry III after his father died.

Entering the vault forces you to walk past a huge wall on which the text of Magna Carta, translated from Latin to English, is embossed.

The text of Magna Carta, translated from Latin to English, is embossed on a huge wall. Clauses that remain in British law today are picked out in gold letters

The clauses that remain in law today are picked out in gold letters, such as the agreement that no free man shall be seized or imprisoned, stripped of his rights or possessions, outlawed, exiled or deprived of his standing without just cause.

It gives a good idea of the uncertainty the king’s subjects previously felt, if they could be banished or thrown in jail at a whim.

The vault is a dark, sombre room that invited hushed voices as you study the faded, yet elegant, decorative characters.

Sadly my inability to read Latin prevented me from lingering too long, but I made up for this by watching an engaging film about the barons’ struggles that is projected on to a wall on the floor below the charter chamber.

The castle is not just a visitor attraction: within its walls sits the city’s Crown Court, built in 1826, where juries still gather to hear modern trials.

A stone’s throw away is a former prison, which has been restored to look as it did when it was used during the Victorian era. It was never a place where convicts served out long sentences, but instead held those found guilty of petty crimes or still awaiting their trial at the adjacent court house.

Thanks to the revamp, visitors can wander in and out of the cells in both male and smaller female blocks, try on replica clothing that the prison staff would have worn and even have a go at typical jail-time activities such as games and lessons.

The most striking exhibit for me was a series of short videos explaning more about certain prisoners’ crimes and motivations.

One boy, aged just seven, was tried for setting fire to a farmer’s haystack and sentenced to 10 years in jail on the Isle of Wight – considered a lenient punishment.

Yet the small building was overcrowded and despite being intended to keep individuals in separate cells, people were squashed into rooms and disease was hard to control.

Little John never reached his intended place of incarceration as he fell sick and died while waiting to be transferred.

Other stories included a pregnant prostitute who inspired a wave of public sympathy and major campaign for her release and a master burglar who successfully escaped the prison – twice.

Visitors can go outside to the small yard where prisoners exercised and there are also exhibits about the lives of the matron and prison governor, who also rarely went outside the building.

Also up on the walls, inside Lucy Tower, is a small graveyard filled with markers bearing initials and dates. These show where prisoners who died inside were laid to rest.

It is possible to walk through the graveyard as part of the circular wall route.

Special events are being organised throughout the summer, with displays inside the grounds and an informative trail of decorated baron statues that will wend through the city centre and up the hill.

Tickets with admission to the Medieval Wall Walk, Victorian Prison and Magna Carta are £12 for adults, £9.60 for concessions and £7.20 for children. Under-fives go free and the castle grounds themselves are free to walk around.

For more details, visit the website www.lincolncastle.com.