The Melbourne Star is offering an exclusive one-hour unlimited ride for 100 Victorian families who are living with cancer, as well as 50 per cent off all single admission tickets for rides taken between 11am and 3pm.

The 100 families invited to take part on Sunday are being supported by Challenge, a Melbourne-based organisation that supports children and their families who are living with cancer. The Melbourne Star has pledged to donate 10 per cent of all single admission ticket sales during that time to Challenge.

The 120-metre-tall wheel - the only giant observation wheel in the southern hemisphere - features 21 enclosed, airconditioned glass cabins which can hold up to 20 people each.

It has welcomed more than 300,000 guests in the past 12 months, with a reported 10 per cent of visitors returning to the attraction. Its busiest day to date was Mother's Day 2014, when it offered free rides to all mothers travelling with their families.

Visitors to the attraction can see views of up 40 kilometres, including the Docklands precinct, Melbourne CBD, Port Phillip Bay and as far as Mount Macedon and the Dandenong Ranges.

Romantics have flocked to the wheel to pop the question, with more than 100 marriage proposals over the past year, rivalling some of the city's most popular places for popping the question. There was also one pop-up wedding.

The wheel features 3½ kilometres of LED lighting with more than 15 million different light combinations. This is reportedly the most advanced LED lighting installation ever created in Melbourne.

The Melbourne Star was conceived as a key addition to the city's skyline and a draw card for many tourists to the world's friendliest city. It has served as a centre point for many major events in the city's calendar including tailored light shows for Valentine's Day, World Aids and the opening night of Les Miserable.

The wheel represents the largest single investment in a tourism attraction in Australia since 1995, Melbourne Star Management Group chief executive Chris Kelly said before it opened in 2013.

However, not all Melburnians have welcomed the wheel with open arms, having noted the many problems the structure faced during construction. Others commented the poor location of the wheel at the less than scenic end of the city.

The Melbourne Star, previously known was the Southern Star, was first opened in December 2008, two years behind schedule. However, it was shut down 40 days later because of major structural defects, with large cracks reported.

The wheel was reconstructed but continued delays meant it did not reopen until December 23, 2013.

The Melbourne Star is open daily from 10am to 10pm, with last admission at 9.30pm. Each ride lasts about 30 minutes.

General admission (single flight) is $32 for adults, $19 for children aged 5 to 15 years, and free for children up to the age of four years old. See melbournestar.com