Charles will first tour The Regimental Museum of The Royal Welsh, the infantry regiment of Wales, in Brecon, Powys.
He will meet school children learning about the regiment's history, as well as families who have donated letters to the museum.
The heir to the throne will then attend Llancaiach Fawr Manor in Trelewis, one of the finest examples of a semi-fortified manor in Wales.
He will visit the 16th century house and gardens, and meet staff, gardeners and volunteers.
His ninth engagement of the tour is The Royal Mint's visitor centre, The Royal Mint Experience, where he will strike a commemorative coin.
The Royal Mint headquarters in Llantrisant, south Wales, was opened by the Queen in 1968 in readiness for the introduction of decimal coinage.