Alright, this is an old and classic MMORPG so people from my generation *should* heard/played it before. I was cleaning up my table this afternoon and found this interesting note that I jotted down years ago regarding a few (Or should I say a lot) interesting places that one should visit in Ragnarok Online.
If you happen to be a player who plays in a private server that supports @warp / !warp command, try these spot and it might surprise you. Either way, some are good hidden map for private GM meeting or event.

Also, as some map are hidden and might not be supported, you may crash if you teleport there. These map will be highlighted with the ** symbol. You have been warned~

yuno 136 319 – Some random roof in Yuno
yuno_in01 168 96
yuno_in01 100 100 – Cozy room
yuno_pre 32 19
ayo_in01 54 18 – Inside a castle I believe
ayo_in02 101 107 – Inside a castle
ama_fild01 336 130
amatsu 276 247

sec_in01 86 102
sec_in01 176 172 – PvP map
sec_in12 22 24
sec_in02 52 162
sec_in02 53 168

kh_vila 28 56 – A VERY beautiful garden
kh_vila 183 71 – Some laboratory
kh_vila 112 183 – King sized bed
prt_in 166 170
prt_church 21 107 – Cementary
prt_castle 319 316
aldebaran 58 238

poring_c01 108 98** – Poring Market
poring_c02 120 217** – Poring Market
quiz_01 167 77** – Good for event etc
quiz_01 247 318** – Good for event etc
lhz_in01 112 173
nif_in 40 174
nif_in 115 172
comodo 154 298 – A stage, good for some event like catwalk
airplane_01 55 66 – Inside a plane

jupe_area1 96 219
jupe_gate 52 138
jupe_ele 37 47
mjolnir_01 315 270 – Dating area
gef_fild12 246 180 – Dating area
gef_fild07 162 245
gon_fild01 260 224 – Baby city!
gon_dun02 81 100
thana_boss 144 129
thana_boss 67 161

himinn 49 46
himinn 49 86
ra_temsky 101 93
ra_temsky 149 132

que_sign01 197 46**
que_sign01 196 44**
que_moon 33 33**
que_moon 166 39**