A £5m footbridge to a dramatic, wind-battered headland that is at the heart of Arthurian legend will this weekend finally open to the public.

The bridge, one of the most ambitious, complicated and at times controversial heritage projects seen in the UK in recent years, will, says English Heritage, restore the lost crossing of Tintagel Castle in north Cornwall.

In practical terms it means visitors will no longer have to climb 148 narrow, steep and often frustratingly busy steps to get round the popular tourist site. Instead they will cross a 68-metre bridge over a spectacular rocky chasm which separates two halves of the remains of the 13th-century castle.

Facebook Twitter Pinterest The bridge means visitors will no longer have to climb 148 steep steps. Photograph: Jim Holden/English Heritage

The bridge’s unusual walking surface consists of 40,000 locally sourced slate tiles, stacked vertically in stainless steel trays. At the centre is a 4cm gap, which will increase in the cold and decrease in the heat but is, the designers say, entirely safe.

“For it to almost close it would have to be 50C for two weeks,” said the bridge’s co-designer William Matthews. “We have designed for extreme temperatures.”

He said people would make whatever they want of the gap. It could be a poetic symbol of stepping from the past to the present, reality to legend, or it could just be the engineering reality of a cantilever bridge. “It’s fun and what is wrong with that?”

Tintagel – in Cornish Din Tagell, meaning “the fortress of the narrow entrance” – is steeped in myth and legend.

Facebook Twitter Pinterest At the centre is a 4cm gap, which will increase in the cold and decrease in the heat but is, the designers say, entirely safe Photograph: Jim Holden/English Heritage

The most evocative is the story of a lust-crazed Uther Pendragon using the crossing to spend the night with Ygerna, during which they conceived Arthur. Ygerna thought Uther was her husband, the Duke of Cornwall, but it was a trick – Uther had been transformed by the wizard Merlin.

That castle may never have existed, but the stories so captured the imagination of Richard, a French-speaking 13th-century Duke of Cornwall, that he built a castle at Tintagel, begun in the 1230s, with the footbridge integral to its design.

The castle probably fell into disrepair by the 1330s and the crossing gradually eroded.

The present-day site attracts 250,000 visitors a year, but the steps were a nightmare for many. It could take 45 minutes to get from one side to the other and be “really frustrating and completely destroy any of the magical feeling of being there”, said Nichola Tasker, English Heritage’s head of national projects. “You are just suddenly annoyed by it.”

The bridge is due to open to the public on Sunday, delayed from Friday because of anticipated severe weather.

It has been welcomed by many and criticised by others. Some have accused English Heritage of the “Disneyfication” of the site. As evidence they point to the bridge and two artworks – a carving of Merlin’s head in the cove and an Arthurian sculpture titled Gallos on the headland.

It is a charge that curators bristle at. “Why it grates for me is because Disney is essentially about making money,” said Georgia Butters, head of historic properties in Cornwall. “What we are trying to do is get people to care about our heritage. We want people to really engage with their heritage, because if you don’t care and you don’t engage, who is going to look after this in another 100 years’ time? That’s why it irritates me.”

The bridge is also late. The castle closed in October and was meant to reopen in the spring. Butters admits they would not have chosen to open in the middle of the summer season.

The lateness is down to how complicated the scheme has been. There is no vehicular access, which meant helicopters had to bring in hundreds of tonnes of materials. Cable cranes normally used in the Swiss Alps were employed to move sections of bridge into place.

The bridge and a wider landscaping project have been made possible by the biggest private donation English Heritage has ever received: £2.5m from Julia and Hans Rausing.

English Heritage expects to see an increase in visitor numbers and has introduced timed ticketing for the site. If anyone misses climbing all those steps, they can still be used.

Facebook Twitter Pinterest English Heritage has been criticised for installing a rock carving of Merlin in the cove beneath the castle. Photograph: David Levene/The Guardian

Matthews, who for 12 years led the design team for the Shard, hopes people will enjoy the bridge, which was co-designed with engineers Ney & Partners in Belgium.

“I don’t know what visitors are going to remember. Some people will say, ‘Oh God, it wobbled.’ Some people will say ‘Oh, the gap was amazing,’ others ‘terrifying’. I don’t know. As long as they go back thinking, ‘That was, fun, what a great day,’ then our job will have been done.”