London always has plenty going on for the discerning, culture-loving visitor, but this weekend the capital will turn into a full-on 48-hour architectural celebration: yes, it is time for the annual London Open House.

Under the umbrella theme 'Revealing', this year's events will offer guests the chance to step inside a staggering 800 buildings, which will be open - freely or via booking - to visitors all across the city.

Many of the recurring favourites will be there, but most importantly, this year sees a slew of brand new buildings opening their doors for the first time. From the box-fresh Leadenhall Building by Rogers Stirk Harbour + Partners, which just got its finishing touches earlier this month, to LSE's RIBA-award winning Saw Swee Hock Student Centre by O'Donnell + Tuomey, there are rich pickings to be had.

And it is not just all about large-scale cultural and commercial work. A number of smaller residential projects, creative conversions, extensions and new builds also feature in the selection, showcasing London's creativity on the domestic front. Other themes to be explored are: 'How the City Works', touching upon question of transport and infrastructure; 'Places and Spaces of the City', examining landscape design; and 'A Greener City', on sustainability.

The architecture buzz has even spilled over into London Fashion Week. Fashion designer Margaret Howell is this year's Design Partner - having supported Open House since 2003 - and worked closely with the initiative for her S/S 2015 show at the Rambert, deftly fusing fashion with architecture. 'This year we needed to move our show to accommodate the growing number of guests,' explains Howell. 'I knew I wanted something with the working space and spirit of our Wigmore Street shop and that's hard to find.'

Here we pick our top twenty buildings to step inside this weekend.