Once in a lifetime – A letter from Richard

Question

This geography-themed standalone crossword has five thematic answers, which are places, sights or landmarks in or around a certain location (a city). Each thematic answer is notable enough to have its own article in the English Wikipedia, although not necessarily under the same name that is used here. The goal is to fill the grid, identify the thematic answers and guess the name of Richard’s destination, which is not indicated in the grid.

Hello Puzzling,

My good friend Gladys asked me to write to you about a pretty unforgettable place I recently visited. I hope you like it. One might say this is a real once-in-a-lifetime experience. I have seen mountains and skyscrapers, been surrounded by places with rich historic and religious significance, and talked to a ton of people who are just as excited to be here as I am. Can you guess where I am?

Wish you were here!
Richard

Across
1. Mountain top all mangled by Oscar engaging in careless run tracking heartless, slug-like fictional slaver (5,2-4)
7. Double-O-Five butted from behind, buried underground (4)
9. Musical group from Iran struggling to entertain Mr Morrison (7)
10. Provide guidance in giving way to Russian river dam (8)
12. Being followed by mysterious British agency, ultimately, one of CIA's members is livid (4)
13. Motown musician is closer to touring with 14 down? (4)
15. (See 17 across)
16. Sci-fi planet's inhabitants cooked peas (4)
17/15. Mother has daughter thrown in horrible jail in connection with unlawful mosque building (6,2-5)
21. Walkways of southern Romania regularly visited by Troy (5)
23. Double-O-Seven protecting Miss Moneypenny? (3)
24. Instrument aiding in the formation of S.P.E.C.T.R.E. temporarily turned over (5)
25. Push through bowel movement (5)
26. Saying "goodness gracious" – a bit archaic, in retrospect (5)
27. US gaming company composer at last showing taste in music (3)
28. Backing powerful politician very forcefully? Excellent tack! (5)
29. I smear the reputation of the Queen exiting Great Britain? (6)
31. Sportsman who's extremely respected – in his game, a god (4)
32. MI6's quartermaster involved in a cruel novel's finish (7)
35. Children's speeches given to an audience without a shred of support (4)
37. Diva's right for messy hair (4)
39. Two letters from Greece mostly contain temperature markings? (8)
40. Singing sea monster scratched bottom eating orca's head and tail, separately (7)
41. Doctrines central to MI6 shown by text message (4)
42. Arab criminal and Chicago crime boss detained by leaders of James Bond's agency inside tall skyscraper complex (5,2,4)

Down
1. After January, Brazilian city university's starting to take place in destroyed 4 down cemetery (6,2-6)
2. Doctor briefs their tactic: getting some documents from the hospital (5,12)
3. He had three daughters to observe, lecherously, in broadcast (4)
4. A senior officer in MI6 touching every flippin' animal (5)
5. Australia finally to sanction Double-O-Three? (5)
6. African God's thanks to religion's follower (5)
7. Mosaic books described by TV's foremost talk show host, with no pressure (5)
8. "Raising agent Bond?" – oaf at aerobics training (11,2,4)
11. Double-O-Nine's been messing with MTV, exchanging one ludicrous extreme for another? That's all good! (14)
14. Over seven decades, they have held concerts in numerous cities (in Germany, especially) (3)
18. Caucasian male escaped complicated structure inspector Banks put up (5)
19/35. Mountain of God linked to war unexpectedly stopped by Latvian native? (5,5)
20. Martin welcoming western ruler (5)
21. Isolate American sailor (4)
22. Large animal, which attacks its prey using its powerful teeth and hot liquid, causes severe damage to the hearing (1-3)
30. Beloved Republican drops out, leading to uproar (3)
33. Advocates argue about losing a schilling (5)
34. Clothing of those who lived in the Andes and rushed around unclimbed peak before middle of day (5)
35. (See 19 down)
36. Joe and Kate got lost, losing track of both edges of expansive wine region (5)
38. Beginning in Uchalinsky, river with length, crossing Russia's southern border (4)

Answer 1

Richard (not Gladys) is in:

MECCA in Saudi Arabia - by the sounds of it, for Hajj: a pilgrimage that Muslims are supposed to take at least once in a lifetime (hence the title). While there, he has visited Jabal al-Nour, Masjid al-Haram, Jannat al-Mu’alla, Abraj Al Bait, and Jabal Thawr.

The completed grid:

Clue explanations:

Across:
1. Mountain top all mangled by Oscar engaging in careless run tracking heartless, slug-like fictional slaver (5,2-4) JABAL AL-NOUR = JA(-b)BA + ALL* + O (Oscar) in RUN*
7. Double-O-Five butted from behind, buried underground (4) TUBE = (_E BUT_)<
9. Musical group from Iran struggling to entertain Mr Morrison (7) NIRVANA = IRAN* around VAN
10. Provide guidance in giving way to Russian river dam (8) OBSTRUCT = (in → OB)STRUCT
12. Being followed by mysterious British agency, ultimately, one of CIA's members is livid (4) (-ci)A + _S _H _Y
13. Motown musician is closer to touring with [Yes]? (4) GAYE = (-tourin)G + AYE (Yes)
15. (See 17 across)
16. Sci-fi planet's inhabitants cooked peas (4) APES = PEAS*
17/15. Mother has daughter thrown in horrible jail in connection with unlawful mosque building (6,2-5) MASJID AL-HARAM = MA’S + D in JAIL* + HARAM (unlawful)
21. Walkways of southern Romania regularly visited by Troy (5) STOAI = S (southern) + T (Troy) + (-r)O(-m)A(-n)I(-a)
23. Double-O-Seven protecting Miss Moneypenny? (3) EVE = _EVE_
24. Instrument aiding in the formation of S.P.E.C.T.R.E. temporarily turned over (5) METER = (_RE TEM_)<
25. Push through bowel movement (5) ELBOW = BOWEL*
26. Saying "goodness gracious" – a bit archaic, in retrospect (5) ADAGE = (EGAD + A)<
27. US gaming company composer at last showing taste in music (3) EAR = EA (US gaming company) + (-compose)R
28. Backing powerful politician very forcefully? Excellent tack! (5) AFFIX = (XI + FF + A)<
29. I smear the reputation of the Queen exiting Great Britain? (6) ISLAND = I + SLAND(-er)
31. Sportsman who's extremely respected – in his game, | a god (4) PELE = ddef
32. MI6's quartermaster involved in a cruel novel's finish (7) LACQUER = Q in ACRUEL*
35. Children's speeches given to an audience without a shred of support (4) TOTS = TO(-a)(-s_)TS
37. Diva's right for messy hair (4) AFRO = (-div)A + FOR*
39. Two letters from Greece mostly contain temperature markings? (8) STIGMATA = S(T)IGMA + TA(-u)
40. Singing sea monster scratched bottom eating orca's head and tail, separately (7) KARAOKE = K(_A)RA(O_)KE(-n)
41. Doctrines central to MI6 shown by text message (4) ISMS = (-m)I(-6) + SMS (text message)
42. Arab criminal and Chicago crime boss detained by leaders of James Bond's agency inside tall skyscraper complex (5,2,4) ABRAJ AL-BAIT = ARAB* + AL (Chicago crime boss) in J_ B_ A_ I_ T_

Down:
1. After January, Brazilian city university's starting to take place in destroyed [llama] cemetery (6,2-6) JANNAT AL-MU’ALLA = JAN + NATAL + U(-niversity) in LLAMA*
2. Doctor briefs their tactic: getting some documents from the hospital (5,12) BIRTH CERTIFICATES = BRIEFSTHEIRTACTIC*
3. He had three daughters to observe, lecherously, in broadcast (4) LEAR = “leer”
4. A senior officer in MI6 touching every flippin' animal (5) LLAMA = (A + M + ALL)<
5. Australia finally to sanction Double-O-Three? (5) OZONE = OZ (Australia) + _O _N _E
6. African God's thanks to religion's follower (5) RASTA = RA’S (African God’s) + TA (thanks)
7. Mosaic books described by TV's foremost talk show host, with no pressure (5) TORAH = T(-v) + O(-p)RAH
8. "Raising agent Bond?" – oaf at aerobics training (11,2,4) BICARBONATE OF SODA = BONDOAFATAEROBICS*
11. Double-O-Nine's been messing with MTV, exchanging one ludicrous extreme for another? That's all good! (14) OMNIBENEVOLENT = OONINE(s → L)BEENMTV*
14. Over seven decades, they have held concerts in numerous cities (in Germany, especially) (3) YES = _Y ES_
18. Caucasian male escaped complicated structure inspector Banks put up (5) AZERI = (-m)AZE + I(-nspecto)R<
19/35. Mountain of God linked to war unexpectedly stopped by Latvian native? (5,5) JABAL THAWR = JA(BALT)H + WAR*
20. Martin welcoming western ruler (5) DEWAN = DE(W)AN
21. Isolate | American sailor (4) SEAL = ddef
22. Large animal, which attacks its prey using its powerful teeth and hot liquid, causes severe damage to the hearing (1-3) T-REX = “tea wrecks”
30. Beloved Republican drops out, leading to uproar (3) ADO = ADO(-red)
33. Advocates argue about losing a schilling (5) URGES = (-a)RGUE* + S (schilling)
34. Clothing of those who lived in the Andes and rushed around unclimbed peak before middle of day (5) RUANA = R(U_)AN + (-d)A(-y)
35. (See 19 down)
36. Joe and Kate got lost, losing track of both edges of expansive wine region (5) TOKAJ = JO(-e)KAT(-e)*
38. Beginning in Uchalinsky, river with length, crossing Russia's southern border (4) URAL = U(-chalinsky) + R (river) + (-russi)A +L (length) &lit!

Also of note:

I believe this is another one of Jafe's 'pangram'-style crosswords, where every letter of the alphabet appears at least once in the grid...