SHUT UP EVERYONE AND READ THIS:
Make a spiral staircase going up the center of the first thing (don't know what to call it). Then, make a bridge across to the second. Then from their again to the main hillside. THIS IS THE ONLY WAY TO ENTER YOUR FORTRESS! Below the bridges and between the "spires", put horrible things like magma, spike pits, shooting ranges for dwarves, etc.
I had just come across a similar map, and was wondering what to do with it, when I read Slappy's suggestion. I had experimented with small spirals in a previous fort, but this was a chance to do it epically My map only has 1 smaller spire, but it does have magma pipe, underground river (with a nice (77 Z) waterfall in it), HFS, sand, no iron (but more goblins that you can shake a stick at).
3Dwarf view:
The bridge you see is the "service" entrance, the trade depot access isn't displayed since 3dwarf apparently doesn't see bridge.
http://www.mkv25.net/dfma/map-5367-giltmurdersFuture plans involve paving the road in that spire (it occasionally grows towercaps otherwise) and attempting to cast the bridge out of obsidian.
World Gen:
Created in DF v0.28.181.40d.
[WORLD_GEN]
[TITLE:NICE SPOT]
[SEED:2882067521]
[HISTORY_SEED:2195186091]
[NAME_SEED:4207536239]
[DIM:33:33]
[END_YEAR:1050]
[BEAST_END_YEAR:50:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:1:400:1600:1600]
[RAINFALL:0:100:51:51]
[TEMPERATURE:25:75:51:51]
[DRAINAGE:0:100:51:51]
[VOLCANISM:0:100:1600:1600]
[SAVAGERY:0:100:51:51]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[GOOD_SQ_COUNTS:1:16:32]
[EVIL_SQ_COUNTS:1:16:32]
[PEAK_NUMBER_MIN:3]
[OCEAN_EDGE_MIN:1]
[VOLCANO_MIN:6]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:75]
[RIVER_MINS:6:6]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:5000]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:1]
[NON_MOUNTAIN_CAVE_MIN:3]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_RIVER:2]
[SHOW_EMBARK_POOL:2]
[SHOW_EMBARK_M_POOL:2]
[SHOW_EMBARK_M_PIPE:2]
[SHOW_EMBARK_CHASM:2]
[SHOW_EMBARK_PIT:2]
[SHOW_EMBARK_OTHER:2]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:15]
[TOTAL_CIV_POPULATION:20000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:136:272:136]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]