Travel writer Colin Thubron was first struck by Islamic architecture when, aged 19, he encountered the Alhambra Palace in Granada, Spain. The palace comprises a series of courtyards, pavilions and alcoves, 'beautifully proportioned and covered by a filigree of plasterwork'. Thubron cites in particular the 'elaborate cupolas of honeycombed decoration - delicate and faded by the light'. He imagined that there must be similar palaces all over the Muslim world and only later realised that the Alhambra was unique.
His second nomination is more obscure. At Gunbad-i Qabus in Iran is a tall brick tower completed in 1006 AD. It is the tomb of a local prince, whose body was suspended from the top of it in a glass coffin. 'I discovered this astonishing building when I was travelling overland to India. It is made up of light coffee-coloured brick flanges which catch the sunlight.' Thubron says it reminds him of 'a stupendous Victorian water tower'.
When he first saw Haghia Sophia in Istanbul (above) Thubron thought it was a 'shambles' but on a later visit he was 'completely riveted by it'. The building began as a church, became a mosque and is now a museum. Its shallow dome is a triumphant example of the early puzzle of setting a dome on a square. 'It is typical of Byzantine architecture as it looks like nothing extraordinary from the outside - all its glory is within, 'says Thubron.