From airport:

A. BY METRO or X95 via Syntagma square + B2 bus to NESTORION (under way pass Sigrou avenue) OR (taxi from Syntagma is recommended for night time)

B. BY X96 EXPRESS BUS from airport to PIRAEUS PORT get off at the bus stop (6, Pliadon str.) "GEFYRA"//"AGIA SKEPI" then walk 850 west along Zefyrou str to Nestorion or by taxi, or next B2 bus or bus 550 bus for 1 bus stop Planetarium (Andrea Sigrou avenue) and then short walk southern behind it to NESTORION.

C. By TAXI/cab  flat rate for Athens following official announcement at the airport and have in mind that the exact fees are shown on the taximeter.
LINKS:
http://athensairportbus.com/en/X96-bus-from-airport-to-piraeus-port.htm/
https://goo.gl/maps/Fb3Uo
The bus station of X96 for Piraeus is located between Exit 4 and 5 at the airport arrivals level.
Express bus X96 departure times from Athens Airport:
00:05, 00:35, 01:05, 01:35, 02:05, 02:35, 03:05, 03:35, 04:05, 04:35, 05:05, 05:35, 06:05, 06:30, 06:55, 07:20, 07:40, 08:00, 08:20, 08:40, 08:55, 09:15, 09:30, 09:50, 10:10, 10:25, 10:50, 11:10, 11:30, 11:50, 12:10, 12:30, 12:50, 13:10, 13:30, 13:50, 14:10, 14:30, 14:45, 15:05, 15:25, 15:45, 16:05, 16:25, 16:45, 17:00, 17:20, 17:40, 18:00, 18:15, 18:35, 18:55, 19:15, 19:35, 19:55, 20:15, 20:35, 20:55, 21:20, 21:45, 22:10, 22:35, 23:05, 23:35
Reminder:
Bus stop for NESTORION Hotel "GEFYRA"//"AGIA SKEPI" please ask the driver to stop at Gefyra//Aghia Skepi street Pleiadon no 6. and not further at Tzitzifies. Call the hotel in case of need.
For night arrival we recommend Bus X95 (terminal Syntagma square) and taxi to NESTORION
ATTENTION:
The final decision for the best option to approach the area and the hotel belongs to the guest and only we give indicative directions and recommendations.
Google maps:
https://goo.gl/maps/zNzb2hvKQtF2
https://goo.gl/maps/edDieYNA14J2 (Airport-Pliadon 6 - Pentelis 8, - 47 min 39 km)
https://goo.gl/maps/JYHJk7MdxBG2 (Pliadon-Pentelis by taxi - 2 min)
https://goo.gl/maps/fnBLPHCV52D2 (Pliadon - Pentelis walking distance 850 meters - 10 min)