Randac is the location where Randac conducted the first Terregenesis. The temple is shown in the comics as being within Attilan. However, it predates Attilan by 18000 years.
25,000 years ago King Randac ruled the Inhumans and invents Terregenesis. 7000 years ago King Myran leads the Inhumans away from humanity and creates Attilan.
The fact that King Randac is so much older than Myran means there could be Inhuman substructures around other than Attilan.
This could be where the Agents of SHIELD are headed if not to Attilan itself.
The temple briefly appears in Uncanny X-Men First Class #1 and 2. Nightcrawler angers the Inhumans by going there. It seems to be the spot where Terregenesis is still occurring.
Inhumans CheatSheet for Agents of SHIELD fans
Who is King Randac of the Inhumans?