A 55m (180ft) high drilling rig has started working at the Eden Project as part of a geothermal power scheme.
The 450-tonne research rig is working to drill down 4.5km (2.8 miles) into granite to test potential power at the Cornwall site as part of a £17m scheme.
If successful, the scheme would use steam created from hot water found deep underground to power turbines and produce electricity.
The first phase of drilling will take about five months.
Once it reaches its target depth, and if tests are successful, another rig nearby would drill a hole of the same depth for producing electricity, bosses said.
Project leader Eden Geothermal Ltd secured £17m funding for the first phase from the European Regional Development Fund, Cornwall Council and investment trust GCP Infrastructure Investments.
Eden Geothermal Ltd chairman Richard Day said it was "thrilling to hear the noise and see the drill bit going round" as work started.
He said: "It's taken a lot of preparation, but we've started now. It's great to see the activity and we're moving forward."
The second phase is due to use steam created from hot water found deep underground to power turbines producing electricity.
The Eden Project said "successfully completing the second phase" would generate enough power for it to become carbon zero by 2023.
The drilling has started on the same week the attraction reopened to visitors after the lifting of some coronavirus restrictions.