Modifiers matching obstruction:

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

Simple categories matching underground:

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