~ Lothering ~
#1. Dane's Refuge - This is the tavern in Lothering where you encounter Leliana. Hard (maybe impossible?) to miss, but if you're going for this achievement, make sure you visit ASAP. Lothering is consumed by the blight early on, and cannot be returned to.
~ Redcliffe ~
#2. Blacksmith - This building, labelled "Blacksmithy" is just off the town square. (The area around the fire where you first enter Redcliffe proper.) You are directed to it in an early quest (the darkspawn attack on the town.)
#3. Dwyn's Home - To the south-east of the town, on the complex of jetties suspended over the water. You are also directed to this location in the attack on Redcliffe.
#4. Kaitlyn's Home - Again, just off the town square. West of Dwyn's Home, your map will help you locate it.
#5. Kaitlyn's Home (Upstairs) - Obviously, just head upstairs in Kaitlyn's Home, sit through a load screen... Aaand, head back downstairs again, 'notha load screen.. (Maybe I should have this game installed?).
#6. Tavern - Easy to miss, this one. It's away from Redcliffe proper, up in the hills on the way to the World Map.
#7. General Store - Another quite missable one, it's south-west along the jetties from Dwyn's Home.
~ Orzammar ~
#8. Proving Grounds - I'm convinced that this refers to the entrance complex before the Proving arena proper, because the related questline can be completed without ever stepping foot in the arena. However, if you want to be sure, and have already completed the related questline, the arena is accessable via a small side-tournament given by a Dwarf within the Proving complex (labelled Proving Armsman). Simply talk to him, take part in a fight, and voila, you've set foot in the proving grounds.
#9. Shaperate - The Shaperate is located in the Diamond Quarter. It is accessable the moment you set foot in Orzammar.
#10. AND #11. Shop - The code is unspecific about WHICH shops must be visited, but I have deduced that one is in the Commons, and the other is in Dust Town. However, to be sure, simply make a thorough sweep of Orzammar (Dust town and The Diamond Quarter included) and enter all available buildings to ensure you check these two.
!! UPDATE : The two shops in question are, without a doubt, FIGOR'S IMPORTS (located in the Commons, it appears to be locked until you've completed some Orzammar main quests.) and ALIMAR'S EMPORIUM (located in Dust Town.) !!
~ Denerim ~
#12. The Pearl - Accessible via the Denerim City map. (The Denerim City Map is accessible via attempting to leave Denerim Market District.)
#13. Gnawed Noble Tavern - Located in Denerim Market District, to the south.
#14. Wonders Of Thedas - Located in Denerim Market District, south west of the Gnawed Noble.
#15. Warehouse - Located in Denerim Market District. (Note, you do NOT need to enter the Warden's Cache (The hidden, inaccessible room hidden behind the bookcases.) for this achievement, merely entering the Warehouse is enough.)
#16. Wade's Emporium - Located in Denerim Market District, centre of the area map.
#17. Dirty Back Alley - As with Locations #18 and #19, this area of the Denerim City Map is only accessible via the Chanters Board Quest "Back Alley Justice."
#18. Dark Alley - See Above.
#19. Rundown Back Street - See Above.
#20. Orphanage - In the Elven Alienage, accessible via Denerim Market District OR Denerim City Map. This location is only available after you have met with Arl Eamon and made your way to the Landsmeet. Upon rescuing Queen Anora, she will inform you of 'Unrest In The Alienage' whereupon you will have an opportunity to visit this location. In the Alienage you will find 'Ser Otto' who, after a little investigation, needs leading through the orphanage.
~ Haven ~
#21. Villager House - To your immediate left as you enter, this empty house is the first structure you will encounter.
#22. Village Shop - This building is directly in front of you as you crest the first hill in Haven, past the Villager House. ( ** This is the only accessible structure in the game to not have a maptag. However, I believe this building may be involved in the main quest anyway.)
~ Final Battle ~
#23. Fort Drakon Rooftop - This location is only accessible in the endgame, whereupon you fight the Archdemon. If you have followed the guide, this achievement should pop on the load screen leading to the Rooftop. Congratulations ^_^