Nine Spinnaker Tower facts you may not know

The 170m-tall Spinnaker Tower in Portsmouth was built in 2005

The Spinnaker Tower is marking 20 years since it opened its doors for the first time.

Costing £35.6m, the Hampshire landmark opened on 18 October 2005, becoming an iconic part of the Portsmouth skyline.

Here are nine things you might not know about the tower.

1) There were three designs

Designs included the Spinnaker, the Triple Tower and the Globe

In 1998, residents of Portsmouth were asked to vote on three different designs for the tower.

They were the Spinnaker, the Triple Tower and the Globe.

About 60% (30,000 people) voted for the Spinnaker, which represents a sail billowing in the wind, reflecting the city's maritime history.

2) Angry football fans demanded a colour change

An artist's impression of plans for the Spinnaker Tower to be painted red

When a sponsorship deal was struck with airline Emirates, plans were revealed to paint the Spinnaker Tower in their corporate colours, red and white.

But a U-turn was made after thousands of furious football fans petitioned against the change.

They were angry because red and white are the colours of Portsmouth's rivals, Southampton FC.

The tower was instead painted blue and gold, with 100 litres of red paint donated to local community groups.

3) The oldest abseiler was 101

'Daring' Doris Long took on the tower ten years ago

Doris Long scaled the Spinnaker Tower in 2015, aged 101, breaking the Guinness World Record for the oldest person to abseil.

Known to many as Daring Doris, she took up the activity when she was 85.

The great-great-grandmother abseiled almost 100m (330ft) to the ground, raising thousands for a local hospice.

She is one of more than 50,000 people who have taken on the challenge.

4) The lift got stuck on opening day

The glass lift on the side of the tower aimed to give visitors views across Portsmouth

David Greenhalgh, Portsmouth City Council's project manager at the time, became trapped in a lift at the Spinnaker Tower for more than an hour on the day it opened.

The external glass lift jammed 100ft (30m) up, and abseiling engineers were called to rescue him.

Following years of technical issues, it was judged unfixable and eventually removed in 2012.

5) It has been the location of 30 gender reveals

In the past, the 170 metre Spinnaker Tower has been lit up in different colours for various reasons, like raising awareness for a cause or charity.

Recently, expectant parents have begun booking the landmark for their babies' gender reveals.

The tower is lit up in a sequence, with its 50 lights flashing blue and pink to build suspense.

It then settles on a final colour - blue for a boy, pink for a girl.

6) It was originally known as the Millenium Tower

Initially it was hoped it would be finished in time for the year 2000

The tower was originally meant to be part of countrywide plans to mark the millennium, alongside structures like the Millenium Dome in London and the Eden Project in Cornwall.

The aim was to create a landmark that would boost tourism in Portsmouth.

Despite being approved by the Millennium Commission in 1995, the project was hindered by political, financial, contractual and construction problems.

It meant building work did not actually begin until after the millennium, in 2001.

It also cost the taxpayer of £11.1m when the public had originally been told it would cost them nothing.

7) The glass floor is three layers thick

Brave visitors can walk across the tower's glass floor

Its glass floor, located in the middle of viewing deck 1 is 60mm (2in) thick with views 100m (328ft) above the harbour.

Made from three layers of glass, it can hold a total weight of 288 stone - the equivalent of two black rhinos.

Members of the public can walk across it, and for a long time it was the largest glass floor in Europe.

8) It was the location of a bold magic trick

In 2017, Southsea magician Dan Churchley performed a daring trick in front of a mesmerised crowd.

The 29-year-old was suspended upside down from the Spinnaker Tower's viewing platform, while wearing a straitjacket.

He managed to free himself in 1 minute and 51 seconds.

9) The tower is built on the seabed

The tower stands on land that once formed part of HMS Vernon, Portsmouth's torpedo training school

The Spinnaker Tower was constructed on the site of a tidal mudflat, which was gradually reclaimed over centuries for naval and dockyard use.

To ensure stability on this soft, reclaimed ground, engineers drove 84 reinforced concrete piles into the seabed - some reaching depths of 50m (164ft).

These deep foundations anchor the tower, allowing it to withstand powerful storms and tides.