"...the lead public body set up to investigate, care for and promote Scotland’s historic environment."
One very cool thing about The Historic Environment Scotland is that they offer what they call The Explorer's Pass. Most of the 77 sites in their care charge an admission to visit. A larger castle such as Edinburgh Castle charges far more than a small castle in a more remote location. If you plan to visit several sites, these costs add up, especially if you are buying tickets for four people. The Explorer's Pass allows you to pay one charge ahead of time and enter as many of these site as you wish over a 5 or 14 day period. We purchased the family package for a 7 day visit over 14 days. This meant that over a 14 day window we could choose 7 days in which to visit a site and allowed us to visit as many sites as we wanted on each of those 7 days. The total cost was 84 pounds which was a steal for us! Edinburgh Castle and Stirling Castle (another great castle!) alone reached a combined cost of 84 pounds, so everything else we did was essentially free! In addition you skip the ticket lines. This isn't a big deal at the smaller castles, but the ticket lines at Edinburgh and Stirling were quite long when we arrived. Skipping them was a great time savor!
We ended up visiting Edinburgh Castle, Stirling Castle, Blackness Castle, Newark Castle, Urquhart Castle, Fort George, Dallas Dhu Historic Distillery, and the Elgin Cathedral. Purchasing the Explorer's Pass was well worth it and something I highly recommend if you intend to visit 3 or more sites operated by The Historic Environment Scotland. For more on The Explorer's Pass and to see a list of which sites are included, go here:
There are other pass options as well if you are visiting just one region of Scotland. We hit several regions, so The Explorer's Pass made the most sense for us.