• Northernmost – Tromsø, Troms og Finnmark. (≈69.695°)
• Southernmost – Lumsden, Southland (≈-45.75°)
• Easternmost – Auckland (let's hope a future trip to Fiji sometime in the near future will change this)
• Westernmost – Point Reyes National Seashore, California

This could go on, but I will hopefully add more to this:

• Longest flight – SYD ^IATA - OSL ^IATA (21.5 hours)
• Closest to equator – Sentosa, Singapore (≈1°)
• Highest point in elevation – Yosemite National Park or Westland Tai Poutini National Park (> 3,100 metres)
• Lowest point in elevation (land) – Badwater Basin, Death Valley (-87 metres)
• Lowest point in elevation (including subsea tunnels) – Oslofjord Tunnel, Oslo (-134 metres)*
• Longest train ride – Sydney - Newcastle (2 hours)
• Longest bus ride – Cairns - Townsville (6 hours)
• Longest journey by bike – Sydney CBD - Parramatta (60+ kilometres)
• Longest trail by foot (timewise) – multiple trails, some of which are private (45 km, 4 days)
• Longest distance on unsealed roads – 253 km (Mungo National Park)
• Highest temperature – 52.5 °C (126.5 °F) (Western Sydney)
• Lowest temperature – −5 °C (23 °F) (Mt Kosciuszko)

*I've been in many subsea Norwegian road tunnels, but cannot find the depth for all tunnels that I've visited