Historic Scotland has identified 1700 "urgent" conservation issues and predicts that any repairs involving scaffolding may not be affordable. The shock findings have been kept from MSPs, with a source at the agency adding that many of the cultural attractions are in a "shocking and dangerous state".
Historic Scotland cares for 345 properties north of the Border, including Edinburgh and Stirling castles. Its estate, which also has abbeys, monuments and museums, is a vital part of Scotland's tourism appeal. Ministers have backed controversial plans to merge the agency with another body, the Royal Commission on the Ancient and Historical Monuments of Scotland.
But the Sunday Herald can reveal that the new organisation that is expected to replace both heritage bodies will inherit a multi-million pound investment backlog.
Two senior Historic Scotland staff - director of conservation David Mitchell, and commercial and tourism director Stephen Duncan - completed an internal report on the state of the sector in February.
The conclusions, which have been obtained by this newspaper, predict that £42m will be required over the next 20 years to conserve buildings. Another £63m will be needed for new infrastructure and facilities relating to the estate, as well as £67m for visitor presentation and tourism, bringing the total to £172.7m.
This figure is "over and above" currently allocated budgets.
The directors flagged up 7500 "medium" and 1700 "urgent" conservation issues. The report warned: "Lack of project funding means that it is increasingly likely they will be generally limited to ground-level works (ie those not requiring scaffolding)."
The directors noted that investment on "basic underlying infrastructure" was"inadequate".
If resources do not become available, the authors argue, it could mean a "loss of historic fabric and leave Historic Scotland exposed to accusations of having different standards for its own properties compared to the other 7700 Ancient Monuments" in Scotland which are not cared for by Historic Scotland.
The directors warned that Edinburgh and Stirling castles have "management issues".
The report, commissioned by the Scottish Government, was completed against a backdrop of funding cuts to Historic Scotland.
Scottish Tory culture spokeswoman Liz Smith said she would write to Culture Secretary Fiona Hyslop "as a matter of urgency".
A spokesperson for Historic Scotland said: "The Government recognises the scale of the challenge across the agency's sites and commissioned this report to get a fuller understanding of the key priorities. This work is ongoing."