Gladys's Word Search Cryptic

_{This is part 7 of the puzzle series. Part 1 is here.}

Dear Puzzling,

I have to say that I didn’t quite get enough of the sun and sea in my last stop, so I’ve decided to come to another place that has plenty of both. Mind you, there is plenty of history here to be admired as well, so you can’t say I’ve just been lying on the beach this whole time!

Hidden inside the grid are seven items belonging to a common theme. Two are plainly visible, albeit not within a single grid entry. Five others have been concealed by changing one letter. You must reveal the hidden items by changing five letters, keeping all grid entries as real words. Once all items have been revealed, the corrected letters reveal the final answer.

In addition, thirteen clues contain an extra word, which you must remove before solving. These extra words together, in clue order, hint at the common theme phonetically. Feel free to make use of this hint or not – you may be able to find out the final answer without it.

Wish you were here!
Love, Gladys.

Across
1. Backer of her father going after the Girl Guide (6)
6. Rebelled Scotch agitator is Englishmen’s prisoner (5)
9. Heated conflict near maritime border (4)
10. Vietnamese revolutionary seen near ancient city for some time (4)
12. Pass by in orderly fashion, please (6)
13. Load off heritable land in the Middle Ages (4)
14. Hamburger’s one to pursue – amino acids, vitamins… finally, protein (6)
16. Humanities award for troubled star (4)
18. The exorcism cases abound (4)
20. A poet with no content for suitable lover (3)
22. Searches for final component in bat by baseball gear producer (9)
24. Ultimately, Mr. Bean commercial is excellent (3)
28. No difference; after returning, Stewart escapes (4)
30. Article about a region (4)
32. Is British king backing state in the Middle East? (6)
34. Bravo! Everyone dance! (4)
35. Two Poles swallowed by snake near one small tree (6)
36. Small part of pale horse’s foot scratched (4)
37. A cat is a fundamental concept in Erwin Schrödinger’s field (4)
38. Vietcong criticizes man-made tracks for birds (5)
39. Do seas corrupt a city on the coast? (6)

Down
2. Hal Jordan’s second ring (4)
3. Schwarzenegger’s role as 21 down’s dominant entertainer having no substance (6)
4. See you occasionally on the southern side of Pennsylvania Avenue (5)
5. One you and I instill feelings of fear and reverence in (3)
6. Greek father character holding in money (5)
7. Retired American doctor with a Jewish headdress (5)
8. Nothing found between two areas in Philippine capital (3)
9. For Manx folk, direction in which to find the Irish stew cooking? (4)
11. Rodent repellent initially placed above a rubber tree top (3)
15. This lesson covers Great Britain and Ireland, among others (5)
16. River sharks’ lunch: cow hearts (4)
17. In fairness, forgetting to improve untidy dwelling? (3)
19. Native Argentine-American can appear at the top (4)
21. Period of time for reaching Proxima Centauri: many seconds (3)
23. Visitors of American clothing retailer given shirt (6)
25. North of Hawaii’s key city (5)
26. Catalogues of string players omitting the top three (5)
27. Mob’s defence supporting individual involved in murder (5)
29. State of dizziness ultimately affects women – and one man (4)
31. "Smoker syndrome"? Marijuana law’s backers unprepared (3)
33. Country boy undressed during a time being lost in Atlas Mountains (4)
34. Drinking establishment to forbid entrance to upright character (3)
35. Life story of sibyl, central character in Greek mythology (3)

_{Gladys will return in Gladys’s Double-Letter Cryptic.}