Modifiers matching obstruction:

• physical,
• electrical,
• hidden,
• surrounding,
• permanent,
• solid,
• impenetrable,
• vertical,
• insurmountable,
• lateral,
• geographic,
• taller,
• urethral,
• raised,
• temporary,
• overhead,
• level,
• visual,
• underground,
• hazardous,
• over,
• rigid,
• nearby,
• unusual,
• significant,
• upright,
• bigger,
• adjacent,
• under,
• mechanical,
• subsurface,
• multiple,
• artificial,
• simple,
• additional,
• low,
• spatial,
• external,
• environmental,
• indoor,
• linear,
• current,
• major,
• discrete,
• immovable,
• irregular,
• elongated,
• outdoor,
• fixed,
• cooler,
• topical,
• internal,
• past,
• relevant,
• hard,
• lighted,
• up,
• visible,
• natural,
• opaque,
• local,
• movable,
• short,
• common,
• tall,
• virtual,
• larger,
• smaller,
• underwater,
• typical,
• small,
• minor,
• isolated,
• metal,
• removable,
• layer,
• dense,
• terrestrial,
• structural,
• nasal,
• horizontal,
• clear,
• hydraulic,
• featureless,
• large,

Simple categories matching underground:

• void,
• feature,
• structure,
• construction,
• area,
• vegetable,
• installation,
• pest,
• topic,
• cable,
• container,
• facility,
• resource,
• relic,
• system,
• formation,
• equipment,
• enclosure,
• work,
• cave,
• location,
• works,
• room,
• pipeline,
• space,
• cavern,
• tank,
• tunnel,
• object,
• plant,
• service,
• music,
• development,
• group,
• organ,
• obstacle,
• property,
• hydrocarbon,
• fortification,
• activity,
• wealth,
• item,
• fixture,
• life,
• obstruction,
• excavation,
• pipe,
• storage,
• line,
• bunker,
• cavity,
• harvester,
• material,
• conduit,
• place,
• cistern,
• expanse,
• stem,
• aquifer,
• part,
• band,
• building,
• utility,
• fluid,
• opening,
• world,
• supply,
• improvement,
• conductor,
• shelter,
• liquid,
• housing,
• reservoir,
• treasure,
• passage,
• duct,