It was to be Europe's tallest residential building, a monument to the boom years when the construction industry helped Spain's economy become one of the fastest growing in the world.

Now, the In Tempo apartment block in Benidorm has become a metaphor for the madness of the 10-year building bonanza that brought the country to its knees.

The 200 metre (650ft) high twin towers containing 269 flats are now the responsibility of the so-called "bad bank" established to consolidate the toxic assets of the country's bankrupt savings banks.

Most of these assets consist of unsold or unfinished property built during the boom. The bank, full name Sociedad de Gestión de Activos de la Restructuración Bancaria (Sareb), assumed the €54m (£47m) In Tempo-related debt of Caixa Galicia, the savings bank that funded the apartments in 2005.

In a symptom of the banking recklessness that had become the norm, Caixa Galicia offered the developer Olga Urbana €93m to build the tower on the strength of the developer putting up a paltry €3,100 in seed capital.

Benidorm has so many tower blocks that from the air it resembles Hong Kong more than the sleepy fishing town it once was. Despite these high-rise buildings, the 47-storey In Tempo, visible from six miles away, dwarfs everything in the area. It has been dogged by contractual problems and in 2011, 13 workers were injured, two of them seriously, when a lift collapsed. Last year workers, angered by continued late payments, refused to enter the site unless they were paid.

The building was due to be completed in 2009. It still remains only 94% finished. Among the many headaches Sareb faces is a long list of creditors and the owners of the 80 flats that have been pre-sold.

The remaining flats will go on the market at a lower price with Sareb saying it is willing to listen to any proposals.

The "bad bank" believes foreign buyers are interested in buying the entire block – but some apparently would only do so if there were no tenants, complicating matters for the existing 80 flat owners.

As well as funding hundreds of thousands of unsold and half-built flats, Spain's savings banks also underwrote numerous white elephants that have contributed to their ruin.

The most notable among these are: the airport at Ciudad Real, with a runway that can accommodate the giant Airbus A380, and another airport at Castellón, neither of which is in operation; the high-speed Toledo to Cuenca rail link, which was shut down for lack of passengers; the City of Culture in Santiago de Compostela, which is in danger of never being completed; and the Oscar Niemeyer-designed International Cultural Centre in Avilés, which has faced a struggle to stay open.

• This article was amended on 18 July 2013 to clarify that the €54m debt taken on by the Sareb bank only refers to Caixa Galicia's In Tempo-related debt, not its total debt.