Roadway tunnel under the runway from Spanish border into Gibraltar, obviating need to close the main access road when runway is in use, with consequent increase in capacity for the airport. To serve this increased capacity, a new terminal is also being built which (I believe) will have an ‘internal border control’ for pax to and from Spain (I believe there will be two entrances, one in Spain and one in Gibraltar). Certainly a popular airport for the Spanish to use and Andalus Airlines now provide services to Madrid and Barcelona in addition to the EasyJet, BA and Monarch services to the UK.
Passed through a few weeks ago and construction is certainly underway and planes are now parking remotely from the existing terminal with pax being bussed to/from. No idea when final completion is due; suggest the Gibraltar Government website for details (although this was well out of date when I last looked).