I got to see the tomb of King Tongmyoung as well as part of my tour. The local guide at the tomb itself, and of course everyone needs to have a local guide at every place visited, was a lady highly knowledgeable in Koguryo history. I did enjoy listening to her. However, as expected, the history told to me was tinged with political undertones. After I had mentioned the name of Tongmyoung's son, which of course I had learnt from a South Korean epic drama serial on the king, the local guide surmised that I must have learnt about the name from sources based on the Samguk Sagi. The DPRK knows the son by a slightly different name.
The Samguk Sagi is a history chronicle compiled during the Koryo period. The team that was responsible for it was unfortunately headed by a descendant of Silla royalty. The DPRK appears to think that the Samguk Sagi was written to belittle Koguryo and lift Silla's reputation.
As further evidence of this belittlement, the local guide pointed out that the Samguk Sagi only lists 12 Koguryo kings when there were in fact, as believed in the DPRK, 17.
By the way, Silla as we know was a southern kingdom and Koguryo was a northern one.
Koguryo appears to be very important to the DPRK and indeed they say that this kingdom was the strongest Korean one ever to have existed. I suppose it was an attractive bit of history too since Pyongyang was a capital of Koguryo.
As for the tomb itself, it was quite massive as compared to other Korean royal tombs, although really new. The temple nearby made for a nice visit.
I had thought that I would get to visit the Kangso Three Tombs too but the itinerary I received was different from the one that the guides had. I was initially somewhat disappointed by this until I learnt from a guide that entering the tomb to see the wall paintings inside would have cost me 100 euros. She said that the paintings were worth every penny. I however believe that almost nothing is worth 100 euros just for a look.