This is just in our opinion and it's not based on a public vote or anything sensible like that.

Our only rule here is that these have to have been built, they can't be wacky ideas that someone has dreamt up that are never actually going to become a reality.

Enjoy!

Sheraton Huzhou Hot Spring Resort, China.

At number five is the crazy looking Sheraton Huzhou Hot Spring Resort in China.

Built on the Taihu Lake near Shanghai, the building's main structure stands 27 storeys tall and houses 282 standard rooms as well as numerous suites.

Whilst the building may appear to be a horseshoe it's actually a complete oval, as further levels hidden underground complete the form.

Bosco Verticale, Italy.

I really like number four; this is Bosco Verticale in Milan and it's just like nothing I've ever seen before.

The literal translation means “vertical forest” and it's easy to see how it acquired that name.

The project is one 18 storey tower and another 26 storey tower planted with over 900 trees across its levels.

They help to moderate the building's temperature in summer and winter, as well as attenuating noise and combating some of the city's smog.

The design was subject to strict load monitoring and wind tunnel testing to ensure that the trees could not topple or be blown over.

30 St Mary Axe, United Kingdom.

In at number three is 30 St Mary Axe in the UK.

Now it's not the tallest building in London by any means but it is, in my opinion, the coolest.

Built on the former site of the Baltic Exchange that was destroyed by a Provisional IRA bomb in the early 90's, the 41 storey tower contains six shafts that twist up through its floors providing natural ventilation.

The tower's form widens as it rises, responding to the tight site constraints at street level.

The Foster and Partners design won the prestigious Stirling Prize in 2004, becoming the first building to do so by unanimous judge's decision.

Turning Torso, Sweden.

Second place for me is a slightly left-of-field entry; the 190m Turning Torso Tower in Sweden.

This building was designed to become a landmark for the country and it certainly achieves that.

The tower's twisting structure is formed of nine, five-storey segments that house office space and 147 apartments.

It reaches a height of 54 storeys in total.

Transamerica Pyramid, United States.

Top place for me actually goes to a bit of an older structure; this is the Transamerica Pyramid in the heart of San Francisco.

Completed in 1972 and standing 48 storeys high, the building is an iconic part of the San Francisco skyline and has featured in many films.

Its pyramid form rises to 260m and two fins on the East and West elevations accommodate a lift and stairwell.

The building's floor plate reduces as it rises meaning that only two of the tower's 18 lifts actually reach the top floor.

The viewing platform is now closed but visitors can access a 360 degree video feed of the view from the ground floor.

Perfect if you're not keen on heights.