Brothers Keith and Eric Kolver are the brains behind Secret Spot.
Keith Kolver said the complex was nearing completion.
"We're still not predicting an opening date as such. There are a few unknowns still."
The pair has a complex set up to draw the water from a nearby spring and heat it up using geothermal heat before it makes its way to the 12 hot tubs.
Keith said once the first part of Secret Spot opened they would consider developing a second stage.
"The second [stage] we'll be talking to the customers to marry up some of the ideas we may have with what they might be saying."
Deputy mayor Dave Donaldson was recently treated to a tour of Secret Spot.
"I'm impressed with the care they are taking to do the development once and do it right.
"It will be a quality experience and that's the way we want our visitor economy to go. A focus on quality, not quantity."
Donaldson said the new plans for Waipa Valley would add to the already popular area.
Mountain Bike Rotorua owner Tak Mutu said the building was behind schedule.
"It's all coming together, just a bit slowly," Mutu said.
"The landlord isn't giving us an opening date but he does say it will be before summer."
Mutu said the development would help further promote mountain biking in Rotorua.
"You only have to look at what it was before we set up eight years ago. There were a couple of portaloos and a busy day was 40 cars. Now every weekend we see a couple of hundred cars out there," he said.
Red Stag Investments managing director Jason Cordes said the project was not "behind schedule as such".
"The main building is a large structure and we've got multiple tenants. It's continuing well.
"It's going to drift into quarter three but the goal was always to open in the 2018/2019 summer."
Cordes said more additions had been made to the original plans which had extended the timeline.
"We've grown it and improved it so it will be a flagship for Rotorua."
The upgrade of Waipa State Mill Rd is almost complete. It will include sealing road verges to provide more car parks.
Rotorua Lakes Council's open spaces manager Rob Pitkethley said the bypass road and the Waipa State Mill road upgrades had a budget of $1.3 million, helped by a grant of $439,000 from Rotorua Energy Charitable Trust.
Pitkethley said work on State Mill Rd had been delayed because of wet weather but was on budget.
