To give yourself any of the following objects in the game for practising purposes use the command "giveinventory #" in the console (accessed using the ` key (below escape)) where # is the desired object number

• 1900 - BoilerKey
• 1920 - IgnitionKey
• 1921 - CorridorKeycard
• 1922 - SiloKeycard
• 1924 - LiftAccessKeycard
• 1925 - BarracksKeycard
• 1932 - PowerCircuit
• 1940 - BlueCrystalKey
• 1941 - RedCrystalKey
• 1942 - Battery
• 1943 - PumpFuse88M
• 1944 - PumpFuse88T
• 1945 - PumpFuse88K
• 1946 - AccessModuleA
• 1947 - AccessModuleB
• 1948 - AccessModuleC
• 1960 - SilverGateKey
• 1962 - Sceptre
• 1963 - GemOfFire
• 1964 - GemOfIce
• 1965 - LavaGlobe

To warp to a specific map for practising use the command "warp #" in the console (accessed using the ` key (below escape)) where # is the desired map number.

• 0 - The Breach
• 1 - Unexpected Help
• 2 - City Streets
• 3 - The Back Alleys
• 4 - Rooftop Journey
• 5 - The Museum
• 6 - Block Party
• 7 - The Sewers
• 8 - To The Subway
• 9 - On The Tracks
• 10 - Train Ride
• 11 - Power Outage
• 12 - Seal The Breach
• 13 - Hole In The Sky
• 14 - The Military Base
• 15 - Corridors Of Pain
• 16 - Main Access
• 17 - Topside
• 18 - Main Access
• 19 - Silo 1
• 20 - Silos 2, 3 and 4
• 21 - Dark Hangar - D
• 22 - Dark Hangar - J
• 23 - The Warehouses
• 24 - Dark Hangar
• 25 - Hit The Lights
• 26 - Into The Barracks
• 27 - The Barracks
• 28 - Rec Room
• 29 - Undersea Observatory
• 30 - The Sub Pen
• 31 - Lost Land Junkyard
• 32 - Metal Mine
• 33 - Plane Wreck
• 34 - The Drain
• 35 - Generator Room
• 36 - The Lab
• 37 - The Dam
• 38 - Into The Jungle
• 39 - The Foyer
• 40 - The Opisthor's Chamber
• 41 - Echoes Of The Past
• 42 - Narrow Passage
• 43 - Ancient Altar
• 44 - Canyon Blockade
• 45 - Bunker Assault
• 46 - Command Centre
• 47 - Final Gate
• 48 - Temple Of The Damned
• 49 - Gate To Oblivion
• 50 - Fiery Encounter
• 51 - Aerial Journey
• 52 - The Nursery
• 53 - Burning Passage
• 54 - Heart Of Fire - End
• 55 - Heart Of Fire - Start
• 56 - Welcoming Committee
• 57 - The Outskirts
• 58 - Chaos Entrance
• 59 - Drilling Sector
• 60 - Ore Transport
• 61 - The Gauntlet
• 62 - Refinery One
• 63 - Central Nexus
• 64 - Staging Area
• 65 - Crystal Processing
• 66 - Refinery Two
• 67 - Undershaft Down
• 68 - Undershaft Halls
• 69 - In The Grasp Of Oblivion

I should put this here in case anyone else needs to know about it: I move the cursor to an option on the game over screen, like 'Load' or 'Quit', then press escape to get back into the game. I tap F1 quite fast and more slowly press the escape key to bring up the escape menu. Go to Options and click or press escape to get out of that screen and you just come back to life with full health. You can use the same technique to open your inventory when you're dead. Just press your inventory key instead of escape when tapping F1. You can even teleport when you're dead by getting out a teleporter from your inventory, then tapping F1 and using E to activate it. It's not helpful if you're killed by a fish in Okasankaar because they just instakill you again before you can react, but it means you don't have to worry too much about dying elsewhere apart from the 7 or 8 seconds it takes to do this.