On his death he laid out complex instructions for dividing his estate; the resulting law-case took years to resolve, effectively preventing the redevelopment of the house and preserving it in its original condition.

[1] Plas Mawr shows a blend of continental Renaissance and local North Wales influences, with an innovative floor-plan and architectural detailing.

The house still retains much of its original plasterwork, which incorporates symbols, badges and heraldry, which the historian Peter Smith has described as "the most perfect and the most complete memorial to Elizabethan Wales.

"[3] The architecture of the house influenced other contemporary projects in North Wales, and was later copied during the 19th and 20th centuries in buildings around the town of Conwy, including the local police station and nearby hotel.

[11] Robert lived in the completed north wing until 1580, when the central and south ranges were built, finishing the main part of Plas Mawr.

[12] Wynne purchased this in 1585, probably for the relatively high price of £40, and demolished it to enable the final phase of development, using the space to build a gatehouse that formed the new entrance to Plas Mawr.

[17] Judging by the details of the roof design, a single master carpenter may have been used for all three parts of the build; he probably worked elsewhere across the region during these years, including on 15 other houses and two churches.

[32] The architects Arthur and Herbert Baker were commissioned to survey the building, conduct repairs and remove some of the post-17th century alterations, and J. R. Furness then carried out conservation work on much of the plasterwork.

[35] The Academy of Art sought government and private assistance to undertake temporary and partial repairs, but these were insufficient and in 1993 it moved into new accommodation and the property was passed into the control of the state, under the management of the Welsh heritage agency Cadw.

[37] Cadw carried out a major restoration project on the house over the next 42 months, combining large scale conservation with detailed surveying and archaeological analysis.

The historian Rick Turner considers Plas Mawr to be "the finest surviving town house of the Elizabethan era" and it is protected under UK law as a Grade I listed building and as a scheduled monument.

[49] Robert Wynn spent time in Germany, and the style of Plas Mawr makes use of North German Gothic themes, particularly in its use of symmetry, the pedimented windows at the front of the house, faceted finials and crow-stepped gables.

[52] Nonetheless, Robert Wynn was only an emerging member of the gentry, and his house was not as large or as sophisticated as contemporary grander Renaissance properties built in larger rural settings.

[49] Some of the house's architecture also reflects the influences from contemporary buildings across North Wales, in particular Gwydir Castle, built by Robert Wynn's father John.

[54] Instead, it has a rear turret, or belvedere, which is raised prominently above the height of the rest of the house, overlooking the town: this was a slightly antiquated feature, but was widely used in other Wynn family properties, including Bodysgallen Hall.

[57] Modern visitors typically enter the house from the High Street to the south, passing through the gatehouse, across the lower courtyard into the hall of the main building.

Probably when Plas Mawr was first built, and certainly by 1665, the hall would have been used to meet ordinary visitors and for servants' meals, rather than forming the main room of the house; the wooden benches and table on display are original to the property.

[62] The service area, including the kitchen and pantry, was instead placed in the centre of the building, between the parlour and the hall; this radical redesign was copied at nearby Hafod Lwyfog.

[54] The attic above the great chamber has a grand timber roof with arch-braced collar trusses, joined using an unusual system called "double pegging", which is only used in the Conwy valley during the late 16th century.

[67] The slope of the land results in Plas Mawr's gardens forming the upper and lower terraces, and these have been replanted and restored in an attempt to show them as they might have appeared in 1665.

[75] The plasterwork also incorporates a number of classical themes, but these are not as well executed as the badges and other emblems: the historian Rick Turner describes them as "rather token additions", and Smith considers this part of the decoration to be "naive".